In English there are only a few words that have just one letter:
- a = the indefinite article – a letter
- I = the first person singular pronoun – I
- o = a blood type; a vocative particle – O, I see an A
A number of other letters are used to represent whole words or parts of words in slang, and other flavours of informal English:
- B = babe, baby
- c = see – I c u (I see you)
- E = ecstasy
- G = gangster, gangsta; grand (1,000)
- k = okay; kilometer
- L = to lose, loss – catching an L (making a loss); loser
- p = pence – 10p = ten pence
- r = are – How r u? (How are you?)
- u = you
- v = very – v good (very good)
- x = kiss
- y = yes, why
Source: Urban Dictionary
In Welsh there are actually quite a few one-letter words, some of which are homographs (written the same, but having different meanings):
- a = who(m), which
- a = interrogative particle before a verb – A ddaeth y dyn? (Did the man come?)
- a = ah!
- a = and
- â = with, by means of
- â = as
- â = he/she/it goes
- e(f) = he, him, it (South Wales)
- i = to, for
- o = from, of, out of
- o = oh!
- o = he, it (North Wales)
- w/ŵ = ooh!
- y = the
- y = relative particle – Canol y dref (town centre / centre of the town)
Welsh – it’s not all long words!
In Swedish there are a few single-letter words:
- å = oh!
- å = small river, stream
- Å = a village in Norrköping municipality, Östergötland, Sweden
- à = at, or – à femtio kronor (at 50 kronor)
- i = in, at, into
- ö = island
- Ö = a locality in Ånge Municipality, Västernorrland County, Sweden
- u = ugh! ooh!
How about in other languages?
This was inspired by a post on the Polyglots Facebook group about single letter words in Swedish.
In Russian: conjunctions а and и; prepositions в (во), к (ко) , о (об), с (со), у; particle ж (reduced version of же); pronoun я (1st pers. sg., “I”; one letter but two phonemes [ja]). There is also two-letter but one-phoneme particle ль (reduced version of ли). That’s not counting interjections (А! О! У!) and (mostly foreign) proper names.
Polish: a (and/but), i (and), o (about), u (at [someone’s place]), w (in), z (with/from)
Spanish has y “and” and o “or”.
Japanese has a bunch of particles which are written with a single syllabic character but require multiple letters when transliterated to the Roman alphabet. The one exception is the direct object marker を, which is pronounced o in official standard Japanese (but wo in some regional speech).
I don’t think you can cite O as a “word” when referring to a blood type. The O is a code, not a word. There is Type A, Type B, Type AB which has both A and B factors, and Type O which has neither A nor B. In a sense, Type O is almost like Type 0 (zero).
The letter O is sometimes seen in biblical and poetic works, and is just an abbreviation for Oh.
In urban acronyms, you might add L for Loser, usually applied in a derogatory way.
Y might be used as a shorthand for WHY, but is commonly used for Yes, with N = No.
Vietnamese: ư (indicating surprise).
In Gaelg (Manx Gaelic), just two single-vowel words: e meaning ‘his’ (when followed by lenition) and ‘her’ (with the radical form of the noun); and y, the definite article, also frequently yn. As far as I know, there are no words that consist of a single consonant.
Italian has ”e” meaning “is”.