Words for slow and related things in Celtic languages.

Words marked with a * are reconstructions.
Proto-Celtic |
*malnos/*mallo- = slow, lazy |
Old Irish (Goídelc) |
mall [mal͈] = slow, tardy, late
utmall = unsteady, restless |
Middle Irish (Gaoidhealg) |
mall = slow, sluggish
mallaigid = to make slow, retard
maill, moill = tardiness, delay
maillech = slowly-moving, leisurely, gentle
admall = very slow, dilatory
immall = very slow, wearisome, sad, sluggish
utmall = unstable, fickle, restless |
Irish (Gaeilge) |
mall [mˠɑul̪ˠ/mˠɑːl̪ˠ/mˠal̪ˠ] = slow, late
mallachar = slowness, dullness, dimness
mallacharach = slow, dim
mallaibh = of late, lately
udhmhall = unstable, restless, unceratin, nimble, quick |
Scottish Gaelic (Gàidhlig) |
mall [maul̪ˠ] = slow, deliberate, placid
mallan [mal̪ˠan] = sluggard, slowcoach
mallanach [mal̪ˠanəx] = slow, dilatory |
Manx (Gaelg) |
moal = slow, sorry, tardy, unimpressive, backward, deliberate, dull, feeble, gradual, meagre |
Etymology: possibly from PIE *mel- (to be late, hesitate) and *-nós (creates verbal adjectives) [source].
Old Irish (Goídelc) |
slaet = heap, layer, pile |
Middle Irish (Gaoidhealg) |
slaet = a swathe, layer, pile, illness, disease
slaetach, slaebach = in layers, sweeping (hair) |
Irish (Gaeilge) |
slaod = swath, layer, flowing mass, prostration, stupefication, float, raft; to mow down, lay low, flow, drag, trail, trudge
slaodach = in swaths, in layers, flowing, prostrating, heavy, oppressive, viscous
slaodacht = viscosity
slaodaí = trudger, slowcoach, lazy-bones
slaodaíocht = trudging, slowness, laziness
slaodchiallach = slow-witted |
Scottish Gaelic (Gàidhlig) |
slaod [sl̪ˠɯːd] = raft, float, sledge, tow, drag, sluggard, slowcoach
slaodach [sl̪ˠɯːdəx] = slow, sluggish, dilatory, dragging, pulling, awkward, clumsy
slaodachadh [sl̪ˠɯːdəxəɣ] = dragging, hauling, slowing down
slaodachd [sl̪ˠɯːdəxg] = slowness, drowsiness, awkwardness |
Manx (Gaelg) |
sleayd = dredge, trail, sledge, trailer
sleaydagh = trailing
sleayder = lug, trailing |
Etymology: unknown [source].
Proto-Celtic |
*aramo- = quiet |
Middle Welsh (Kymraec) |
araf, arav [ˈarav] = slow, leisurely, calm, quiet
arafu = to be(come) or make slow, slow down
arafaidd, arauaidd = slow, gradual, mild, gentle
arafhau = to make or become quiet or calm, |
Welsh (Cymraeg) |
araf [ˈarav] = slow, gradual, tedious, tiresome, mild, meek, gentle, tender
arafu = to be(come) or make slow, slow down, retard
arafaidd = slow, gradual, mild, gentle, lovely, pleasant
arafedd = slowness, gentleness, tenderness
arafhau = to make or become quiet or calm, ease, abate, moderate
arafol = slow, gradual, slowing, delaying |
Etymology: from PIE *h₁r̥h₃-mo-, from *h₁reh₃- (rest). Words from the same roots include Ruhe (calm, quietness, rest) in German, ro (calmness) in Danish, ro (peace, quiet, tranquility) in Swedish, and unruly in English [source].
Proto-Brythonic |
*segʉr = idle |
Middle Welsh (Kymraec) |
segur = idle
segyra, segura, seguru, segvro = to (be) idle
segyrllyt, segurllyd = idle, lazy, sluggish, slothful |
Welsh (Cymraeg) |
segur [ˈsɛɡɨ̞r / ˈseːɡɪr] = idle, unoccupied, inactive, lazy, slothful, disused, idle
seguro = to (be) idle, laze, linger, lounge around, rest
segurdod = idleness, laziness
segurllyd = idle, lazy, sluggish, slothful
segurwr = idler, lazy person |
Middle Cornish (Cernewec) |
sigyr, zigyr = sluggish, lazy |
Cornish (Kernewek) |
syger = idle, lazy, lethargic, slow
sygera = to seep, trickle
sygerans = seep(age)
sygerneth = idleness, laziness, lethargy
sygerus = at leisure, leisurely |
Etymology: from Latin sēcūrus (careless, carefree, negligent, safe, secure), from sē- (without) and cūra (care). Words from the same root include secure and sure in English, sicuru (safe, secure, sure) in Italian, seguro (secure, safe, sure) in Spanish and säker (safe, secure, sure, certain) in Swedish [source].
Proto-Celtic |
*uɸostatos = stable |
Old Irish (Goídelc) |
fossad = firm, steady |
Middle Irish (Gaoidhealg) |
fossad, fossud = stationary, fixed, firm, steady, steadfast, consistent, flat surface, level place, stopping-place, abode |
Irish (Gaeilge) |
fosadh = stop, stay, rest, stable position, steadiness, stability |
Scottish Gaelic (Gàidhlig) |
fosadh [fɔsəɣ] = cessation, desisting, recess, respite, (act of) abiding |
Proto-Brythonic |
*gwostad = (?) |
Middle Welsh (Kymraec) |
gwastat, guastat = flat, level, smooth |
Welsh (Cymraeg) |
gwastad [ˈɡwastad] = flat, level, smooth, even, horizontal, continual, constant, quiet, peaceful, gentle, plain, level |
Cornish (Kernewek) |
gwastas = flat, open, plain, smooth |
Middle Breton (Brezonec) |
goustat, goustadic, goustadec, goustadic = gently, slowly |
Breton (Brezhoneg) |
gou(e)stad = slow, slowly
doustadik = slow, slowly |
Etymology: unknown [source].
Another word for slow in Cornish is lent, and lenthe means to slow down. This is possibly from (Old) French lent (slow), or from Latin lentus (sticky, slow, flexible).
In Middle Cornish the word hel means slow or tardy, and cosel/kozal means soft, quiet, slow or sluggish, which became kosel (calm, quiet, restful, still, tranquil) in revived Cornish.
Another Proto-Celtic word for slow is *dwāyo-. This became doé / doe (slow, sluggish) in Old Irish and Middle Irish, but has no descendents I can find in the modern Celtic languages.

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, Lexicon Cornu-britannicum: A Dictionary of the Ancient Celtic Language of Cornwall, Dictionaire Favereau, TermOfis, Le dictionnaire diachronique du breton, Etymological Dictionary Of Proto Celtic