Words for sweet and related things in Celtic languages.

Words marked with a * are reconstructions.
| Proto-Celtic |
*melissis, *melisti = sweet |
| Old Irish (Goídelc) |
milis [ˈmʲilʲisʲ] = sweet |
| Middle Irish (Gaoidhealg) |
milis = sweet, fresh (water) |
| Irish (Gaeilge) |
milis [ˈmʲɪlʲɪʃ] = sweet, tender, tasty, fresh (water); honeyed (words), flattering
milisbhriathrach = sweet-spoken, honey-tongued
milisín = sweet morsel
milseán = sweet, bonbon, candy; sweet dish, dessert
milseog = dessert; sweetheart, darling
milsigh = to sweeten
uisce milis = sweet/fresh water
teange mhilis = flattering tongue |
| Scottish Gaelic (Gàidhlig) |
milis [milɪʃ] = sweet; melodious, musical; flattering
aran-milis = gingerbread
baine milis = sweet milk, condensed milk
buntàta milis = sweet potato, yam
coirce-milis = sweet corn, maize
slaman-milis = jelly |
| Manx (Gaelg) |
millish = sweet, darling, sugary, dulcet, honeyed, luscious, fruity, balmy
bee millish = sweetmeat, sweet
feddan millish = recorder, fipple flute
fooillagh millish = trifle
slumm millish = jelly
ushtey millish = fresh water
focklyn millish = honeyed words |
| Proto-Brythonic |
*melɨs = sweet |
| Middle Welsh (Kymraec) |
melis, melys = sweet, pleasant-tasting, delicious
meledic = sweetened with honey
melysvwyt, melysvwyd, melys-fwyd = sweet food, sweet dish, delicacy, dainty food, sweetmeat, dessert
melûsrwyth, melyssrwydd = sweetness, sweet or delicious taste |
| Welsh (Cymraeg) |
melys [ˈmɛlɨ̞s/ˈmeːlɪs/ˈmɛlɪs] = sweet, pleasant-tasting, delicious, tasty; not salty, fresh (water); delightful, agreeable, pleasant, charming; sweet-sounding, euphonious, melodious; sweet-smelling, fragrant
dant melys = sweet tooth
pethau melys = sweets
tatws melys = sweet potato
melysaf, meluso = to sweeten, mitigate, alleviate
melysaidd, melusaidd = rather sweet, delightful, agreeable
melyfwyd, melusfwyd = sweet food, sweet dish, delicacy, dainty food, sweetmeat, dessert
melyfwyd, melusfwyd = sweet, delicious, delightful, agreeable, pleasant, melodious, fond of sweet food or drink, greedy, voracious
melysrwydd, melusrwydd = sweetness, sweet or delicious taste, melodiousness, fondness for delicate food |
| Cornish (Kernewek) |
melys [‘mɛlɪs/’mɛləʃ] = very sweet, honeyed
kleves melys = diabetes |
| Old Breton (Brethonoc) |
milis = honeyed |
| Middle Breton (Brezonec) |
milis = honeyed, sweetish, sneaky |
| Breton (Brezhoneg) |
melis, milis = honeyed |
Etymology: from Proto-Indo-European *mélid (honey)), which is also the root of the English words mildew and mulch [source].
| Proto-Celtic |
*su̯eko-s = to smell (good) |
| Middle Welsh (Kymraec) |
chwech = sweet
wech, chweg, chwec = sweet, lucious, pleasant, comely |
| Welsh (Cymraeg) |
chwech [χweːχ/hweːχ] = sweet
chweg = sweet, lucious, pleasant, comely
chwegaidd = sweetish
chwegrwydd = sweetness, lusciousness |
| Middle Cornish (Cernewec) |
hwec, hwecah, hweg, hwêg, whêk = sweet, pleasant, dear
hwecter, whecter = sweetness, pleasantness, suavity, delight
hwegol, whegol = dear |
| Cornish (Kernewek) |
hweg = sweet, dear, gentle, kind, nice, pleasant, pleasing
hwegednow, hwegnnow = candy
hwegen = darling, pet, lozenge, sweet
hwegoll = darling, delightful, sweetest
hwegys = sweetcorn, maize
hweg-oll = darling, delightful, sweetest
ys hweg = sweetcorn, maize |
| Middle Breton (Brezonec) |
huec = sweet, delicate |
| Breton (Brezhoneg) |
c’hwek [xweːk] = soft, suave, sugar, delicious, exquisite, pleasant
c’hwekaat = to sweeten
c’hwekted [ˈxwek.tet] = softness, suavity
c’hwekter = delicacy
mel c’hwek = sweet honey
gwin c’hwek = sweet wine |
Etymology: unknown
The usual Breton word for sweet is dous, which probably comes from the Old French dous (soft, tender), form the Latin dulcis (sweet, fragrant, melodious), from the Proto-Indo-European *dl̥kú- (sweet) [source].

Sources: Wiktionary, Am Faclair Beag, Online Manx Dictionary, Teanglann.ie, eDIL – Electronic Dictionary of the Irish Language, In Dúil Bélrai English – Old Irish glossary, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionaire Favereau, TermOfis, English – ProtoCeltic WordList (PDF), Etymological Dictionary Of Proto Celtic