After starting my previous post with this question but not answering it, I’ll get straight to the point. There is a tie for first place, with two episode titles that are two characters long:

Shortest episode titles

Title	Length	Series	Episode
Q2	2 letters	Voyager	7x19
E²	2 letters	Enterprise	3x21

The shortest title per series is:

Title	Length	Series	Episode
Miri	4 letters	The Original Series	1x11
Bem	3 letters	The Animated Series	2x02
Qpid	4 letters	The Next Generation	4x20
Dax	3 letters	Deep Space Nine	1x08
Q2	2 letters	Voyager	7x19
E²	2 letters	Enterprise	3x21

Every series has several single word episode titles.

See them all

Title	Length	Series	Episode
Miri	4 letters	TOS	1x11
Arena	5 letters	TOS	1x19
Catspaw	7 letters	TOS	1x01
Metamorphosis	13 letters	TOS	1x02
Obsession	9 letters	TOS	2x18
Yesteryear	10 letters	TAS	1x02
Bem	3 letters	TAS	2x02
Albatross	9 letters	TAS	2x04
Haven	5 letters	TNG	1x05
Justice	7 letters	TNG	1x09
Battle	6 letters	TNG	1x10
Datalore	8 letters	TNG	1x14
11001001	8 letters	TNG	1x16
Symbiosis	9 letters	TNG	1x22
Conspiracy	10 letters	TNG	1x25
Contagion	9 letters	TNG	2x11
Manhunt	7 letters	TNG	2x19
Evolution	9 letters	TNG	3x01
Allegiance	10 letters	TNG	3x18
Sarek	5 letters	TNG	3x23
Transfigurations	16 letters	TNG	3x25
Family	6 letters	TNG	4x02
Brothers	8 letters	TNG	4x03
Legacy	6 letters	TNG	4x06
Reunion	7 letters	TNG	4x07
Clues	5 letters	TNG	4x14
Qpid	4 letters	TNG	4x20
Redemption	10 letters	TNG	4x26
Darmok	6 letters	TNG	5x02
Disaster	8 letters	TNG	5x05
Unification	11 letters	TNG	5x07
Violations	10 letters	TNG	5x12
Conundrum	9 letters	TNG	5x14
Ethics	6 letters	TNG	5x16
Relics	6 letters	TNG	6x04
Schisms	7 letters	TNG	6x05
Rascals	7 letters	TNG	6x07
Aquiel	6 letters	TNG	6x13
Tapestry	8 letters	TNG	6x15
Birthright	10 letters	TNG	6x16
Lessons	7 letters	TNG	6x19
Suspicions	10 letters	TNG	6x22
Timescape	9 letters	TNG	6x25
Descent	7 letters	TNG	6x26
Liaisons	8 letters	TNG	7x02
Interface	9 letters	TNG	7x03
Gambit	6 letters	TNG	7x04
Phantasms	9 letters	TNG	7x06
Attached	8 letters	TNG	7x08
Inheritance	11 letters	TNG	7x10
Parallels	9 letters	TNG	7x11
Homeward	8 letters	TNG	7x13
Masks	5 letters	TNG	7x17
Genesis	7 letters	TNG	7x19
Firstborn	9 letters	TNG	7x21
Bloodlines	10 letters	TNG	7x22
Emergence	9 letters	TNG	7x23
Emissary	8 letters	DS9	1x01
Babel	5 letters	DS9	1x05
Q-Less	6 letters	DS9	1x07
Dax	3 letters	DS9	1x08
Vortex	6 letters	DS9	1x12
Storyteller	11 letters	DS9	1x14
Progress	8 letters	DS9	1x15
Forsaken	8 letters	DS9	1x17
Duet	4 letters	DS9	1x19
Cardassians	11 letters	DS9	2x05
Melora	6 letters	DS9	2x06
Sanctuary	9 letters	DS9	2x10
Rivals	6 letters	DS9	2x11
Whispers	8 letters	DS9	2x13
Paradise	8 letters	DS9	2x14
Shadowplay	10 letters	DS9	2x15
Crossover	9 letters	DS9	2x23
Tribunal	8 letters	DS9	2x25
Equilibrium	11 letters	DS9	3x04
Meridian	8 letters	DS9	3x08
Defiant	7 letters	DS9	3x09
Fascination	11 letters	DS9	3x10
Destiny	7 letters	DS9	3x15
Visionary	9 letters	DS9	3x17
Explorers	9 letters	DS9	3x22
Shakaar	7 letters	DS9	3x24
Facets	6 letters	DS9	3x25
Indiscretion	12 letters	DS9	4x05
Rejoined	8 letters	DS9	4x06
Homefront	9 letters	DS9	4x11
Crossfire	9 letters	DS9	4x13
Accession	9 letters	DS9	4x17
Rapture	7 letters	DS9	5x10
Resurrection	12 letters	DS9	6x08
Waltz	5 letters	DS9	6x11
Inquisition	11 letters	DS9	6x18
Valiant	7 letters	DS9	6x22
Afterimage	10 letters	DS9	7x03
Chrysalis	9 letters	DS9	7x05
Covenant	8 letters	DS9	7x09
Chimera	7 letters	DS9	7x14
Penumbra	8 letters	DS9	7x17
Caretaker	9 letters	VOY	1x01
Parallax	8 letters	VOY	1x03
Phage	5 letters	VOY	1x05
Emanations	10 letters	VOY	1x09
Cathexis	8 letters	VOY	1x13
Faces	5 letters	VOY	1x14
Jetrel	6 letters	VOY	1x15
Initiations	11 letters	VOY	2x02
Projections	11 letters	VOY	2x03
Elogium	7 letters	VOY	2x04
Twisted	7 letters	VOY	2x06
Parturition	11 letters	VOY	2x07
Tattoo	6 letters	VOY	2x09
Maneuvers	9 letters	VOY	2x11
Resistance	10 letters	VOY	2x12
Prototype	9 letters	VOY	2x13
Alliances	9 letters	VOY	2x14
Threshold	9 letters	VOY	2x15
Meld	4 letters	VOY	2x16
Dreadnought	11 letters	VOY	2x17
Lifesigns	9 letters	VOY	2x19
Investigations	14 letters	VOY	2x20
Deadlock	8 letters	VOY	2x21
Innocence	9 letters	VOY	2x22
Tuvix	5 letters	VOY	2x24
Resolutions	11 letters	VOY	2x25
Basics	6 letters	VOY	2x26
Flashback	9 letters	VOY	3x02
Remember	8 letters	VOY	3x06
Warlord	7 letters	VOY	3x10
Macrocosm	9 letters	VOY	3x12
Coda	4 letters	VOY	3x15
Unity	5 letters	VOY	3x17
Darkling	8 letters	VOY	3x18
Rise	4 letters	VOY	3x19
Displaced	9 letters	VOY	3x24
Scorpion	8 letters	VOY	3x26
Nemesis	7 letters	VOY	4x04
Revulsion	9 letters	VOY	4x05
Hunters	7 letters	VOY	4x15
Prey	4 letters	VOY	4x16
Retrospect	10 letters	VOY	4x17
Unforgettable	13 letters	VOY	4x22
Demon	5 letters	VOY	4x24
One	3 letters	VOY	4x25
Night	5 letters	VOY	5x01
Drone	5 letters	VOY	5x02
Timeless	8 letters	VOY	5x06
Counterpoint	12 letters	VOY	5x10
Gravity	7 letters	VOY	5x13
Bliss	5 letters	VOY	5x14
Juggernaut	10 letters	VOY	5x21
11:59	5 letters	VOY	5x23
Relativity	10 letters	VOY	5x24
Warhead	7 letters	VOY	5x25
Equinox	7 letters	VOY	5x26
Alice	5 letters	VOY	6x05
Riddles	7 letters	VOY	6x06
Pathfinder	10 letters	VOY	6x10
Virtuoso	8 letters	VOY	6x13
Memorial	8 letters	VOY	6x14
Tsunkatse	9 letters	VOY	6x15
Collective	10 letters	VOY	6x16
Muse	4 letters	VOY	6x22
Fury	4 letters	VOY	6x23
Imperfection	12 letters	VOY	7x02
Drive	5 letters	VOY	7x03
Repression	10 letters	VOY	7x04
Nightingale	11 letters	VOY	7x08
Shattered	9 letters	VOY	7x11
Lineage	7 letters	VOY	7x12
Repentance	10 letters	VOY	7x13
Prophecy	8 letters	VOY	7x14
Workforce	9 letters	VOY	7x16
Q2	2 letters	VOY	7x19
Homestead	9 letters	VOY	7x23
Endgame	7 letters	VOY	7x25
Unexpected	10 letters	ENT	1x05
Civilization	12 letters	ENT	1x09
Fusion	6 letters	ENT	1x17
Acquisition	11 letters	ENT	1x19
Oasis	5 letters	ENT	1x20
Detained	8 letters	ENT	1x21
Shockwave	9 letters	ENT	1x26
Minefield	9 letters	ENT	2x03
Marauders	9 letters	ENT	2x06
Singularity	11 letters	ENT	2x09
Dawn	4 letters	ENT	2x13
Stigma	6 letters	ENT	2x14
Canamar	7 letters	ENT	2x17
Judgment	8 letters	ENT	2x19
Horizon	7 letters	ENT	2x20
Cogenitor	9 letters	ENT	2x22
Regeneration	12 letters	ENT	2x23
Bounty	6 letters	ENT	2x25
Anomaly	7 letters	ENT	3x02
Extinction	10 letters	ENT	3x03
Rajiin	6 letters	ENT	3x04
Impulse	7 letters	ENT	3x05
Exile	5 letters	ENT	3x06
Twilight	8 letters	ENT	3x08
Similitude	10 letters	ENT	3x10
Stratagem	9 letters	ENT	3x14
Harbinger	9 letters	ENT	3x15
Hatchery	8 letters	ENT	3x17
Damage	6 letters	ENT	3x19
E²	2 letters	ENT	3x21
Countdown	9 letters	ENT	3x23
Home	4 letters	ENT	4x03
Borderland	10 letters	ENT	4x04
Forge	5 letters	ENT	4x07
Awakening	9 letters	ENT	4x08
Kir’Shara	9 letters	ENT	4x09
Daedalus	8 letters	ENT	4x10
United	6 letters	ENT	4x13
Affliction	10 letters	ENT	4x15
Divergence	10 letters	ENT	4x16
Bound	5 letters	ENT	4x17
Demons	6 letters	ENT	4x20

Longest episode titles

Unlike with the shortest episode title, I had a good idea what the longest one was. At least, I had two candidates, but without sitting down and counting, picking one would have been a guess. I can confirm they are the longest two, and I present them both since they are such outliers compared to the rest.

Title	Length	Series	Episode
For the World is Hollow and I Have Touched the Sky	50 letters	The Original Series	3x10
Looking for par’Mach in All the Wrong Places	44 letters	Deep Space Nine	5x03

And the longest per series:

Title	Length	Series	Episode
For the World is Hollow and I Have Touched the Sky	50 letters	The Original Series	3x10
How Sharper Than a Serpent’s Tooth	34 letters	The Animated Series	2x05
Where No One Has Gone Before	28 letters	The Next Generation	1x06
Looking for par’Mach in All the Wrong Places	44 letters	Deep Space Nine	5x03
The Haunting of Deck Twelve	27 letters	Voyager	6x25
Two Days and Two Nights	23 letters	Enterprise	1x25

This brings us our first controversial result. I decided that ellipses should be treated as a single letter (if only for a sense of typographical superiority). In this case, treating it as three letters would produce a different result:

Title	Length	Series	Episode
These Are the Voyages…	24 letters	Enterprise	4x22

The titles so far have been longest by letter-count. Longest by word-count can also be determined. This gives identical results, except Voyager and the Animated Series now have ties:

Title	Length	Series	Episode
For the World is Hollow and I Have Touched the Sky	11 words	The Original Series	3x10
One of Our Planets is Missing	6 words	The Animated Series	1x03
How Sharper Than a Serpent’s Tooth	6 words	The Animated Series	2x05
Where No One Has Gone Before	6 words	The Next Generation	1x06
Looking for par’Mach in All the Wrong Places	8 words	Deep Space Nine	5x03
The Q and the Grey	5 words	Voyager	3x11
Someone to Watch Over Me	5 words	Voyager	6x25
The Haunting of Deck Twelve	5 words	Voyager	5x22
Two Days and Two Nights	5 words	Enterprise	1x25