English words without vowels
English orthography typically represents vowel sounds with the five conventional vowel letters , as well as , which may also be a consonant depending on context. However, outside of abbreviations, there are a handful of words in English that do not have vowels, either because the vowel sounds are not written with vowel letters or because the words themselves are pronounced without vowel sounds.

Words without written vowels
There are very few lexical words (that is, not counting interjections) without vowel letters. The longest such lexical word is tsktsks, pronounced . The mathematical expression nth , as in delighted to the nth degree, is in fairly common usage. Another mathematical term without vowel letters is ln, the natural logarithm. A more obscure example is rng , derived from ring by deleting the letter . 
Vowelless proper names from other languages, such as the surname Ng, may retain their original spelling, even if they are pronounced with vowels.

In the Middle English period, there were no standard spellings, but  was sometimes used to represent either a vowel or a consonant sound in the same way that Modern English does with , particularly during the 14th and 15th centuries. This vocalic  generally represented , as in wss ("use"). However at that time the form  was still sometimes used to represent a digraph  (see W), not as a separate letter. In modern Welsh, "W" is simply a single letter which often represents a vowel sound. Thus words borrowed from Welsh may use  this way, such as:
 The crwth (pronounced  or , also spelled cruth in English) is a Welsh musical instrument similar to the violin.
He intricately rhymes, to the music of crwth and pibgorn.
 cwtch (a hiding place or cubby hole) is also from Welsh (albeit a recent word influenced by English, and used almost exclusively in the variant of English spoken in Wales, not in standard English), and crwth and cwtch are the longest English dictionary words without  according to Collins Dictionary.
 A cwm (pronounced ) is used in English in a technical geographical or mountaineering context to mean a deep hollow in a mountainous area, usually with steep edges on some sides, like a corrie or cirque, such as the Western Cwm of Mount Everest. It is also sometimes used, by way of more recent borrowing from Welsh, in a more general sense of a valley. The spellings coombe, combe, coomb, and comb come from the Old English cumb, which appears either to be a much earlier borrowing from a predecessor of modern Welsh, or to have an even earlier origin, given that there was an ancient Greek word κὑμβη (kumbē) meaning a hollow vessel. In English literature, one can find the spellings combe (as in Ilfracombe and Castle Combe), coomb (as in J. R. R. Tolkien) or comb (as in Alfred, Lord Tennyson).

There are also numerous vowelless interjections and onomatopoeia found more or less frequently, including brr or brrr, bzzt, grrr, hm, hmm, mm, mmm, mhmm, sksksksk, pfft, pht, phpht, psst, sh, shh, zzz. It is questionable whether any of these are words: they are sequences of letters used to imitate a sound, and there is no limit to how many such sequences could be constructed.

Alphabetical list of words not containing the main 5 vowels but including Y 
Some of these are merely interjections, some promoted by comic magazines (see above}. Many others are borrowed or derived from other languages, most commonly Greek, e.g. glyph (Greek), skyr (Icelandic), fyrd (Anglo-Saxon).

 By(s)
 Byrl(s)
 Chynd
 Cly
 Cry
 Crypt(s)
 Cyst(s)
 Dry(ly)(s)
 Fly
 Flyby(s)
 Fry
 Fy
 Fyrd(s)
 Ghyll(s)
 Glycyl(s)
 Glyph(s)
 Gym(s)
 Gyp
 Gyppy
 Gyp(s)
 Gypsy
 Hwyl(s)
 Hymn(s)
 Hyp(s)
 Jynx
 Ky
 Lym(s)
 Lymph(s)
 Lynch
 Lynx
 My
 Myrrh(s)
 Myth
 Ny(s)
 Nymph(ly)(s)
 Ply
 Pry(s)
 Psych
 Pygmy
 Pyx
 Rhy
 Rhythm(s)
 Rynd(s)
 Scry
 Shy(ly)
 Sky
 Skyr
 Sly(ly)
 Spry(ly)
 Spy
 Sty
 Stymy
 Swy
 Sylph(s)
 Syn
 Sync(s)
 Synch(s)
 Synd(s)
 Sybyzgy
 Syzygy
 Thy
 Thymy
 Try
 Tryp(s)
 Tryst(s)
 Twyndyllyng(s)
 Tyg(s)
 Typp(s)
 Tyyn
 Vly
 Why(s)
 Wyn(s)
 Wynn
 Wry (ly)
 Wych
 Wyn
 Wynd(s)
 Wynn(s)
 Xylyl(s)
 Xyst(s)
 Ympt

Alphabetical list of words without the main vowels and also excluding Y 

 Brr
 Brrr
 Bzzt
 Ch
 Crwth(s)
 Cwm(s)
 Cwtch
 Grr
 Grrl(s)
 Grrr
 Grrrl(s)
 Hm
 Hmph
 Hmm
 Hmmm
 Mhmm
 Mm
 Mmm
 Nth
 Pfft
 Phpht
 Pht
 Psst
 Pwn(s)
 Rng
 Sh
 Shh
 Sknch 
 Sksksksk
 Tsk(s)
 Tss
 Tsktsk(s)
 Twp
 Zzz

Words without vowel sounds
Weak forms of function words may be realized without vowel sounds, as in I can go  and I must sell . Some of these forms are reflected in orthography as contractions, such as s, ll, d, and n't.

See also
 Wiktionary:List of words that comprise a single sound
 
 Words without vowels in other languages

References

Types of words
Vowels
Vowel letters
Lists of English words