Tw trw, mon vieux!

here are a few more than swim into focus:

pwll = pool
drws = door
drwg = bad or naughty
drwm = drum
dwbl = double
gwrth = counter or contra
gwr = man (and interestingly gwrach = witch!)
lwc = luck
llwgr = corruption
dwl = dull, stupid
dwndwr = hubub, babble
dwthwn = day (tho around here we woud use dydd)
llwnc = gulp, swallow
dwrn = fist, handle, hilt
llwm = bare, destitute
mwrthwt = hammer
cwrw - BEER!
wydd = goose (I think this is a soft mutation of gwydd)
cwn = dog or dogs (depending on where in Wales)
cwl = cool, wicked (modern transliteration)
cwrwgl = coracle (traditional withy & skin fishing boat)
mwlwg = refuse, sweepings
mwng - mane (horse's)
pwt = short ('Gog' or North Welsh)
cwcw = cuckoo
cwpl = couple; tie-beam
cwmwl = cloud
cwt is one that I like since it has quite varied meanings depending on context: tail, skirt, queue, hut, sty - the common feature seems to be something as an appendage.
cwr = edge, border or skirt, whereas cwrs = course
mwrllwch = fog, mist, vapour (another Gog term, my kids said)

and one for Dr Bill (YCLIU!): cwthwm

if that's not more 'w' stuff than you ever wanted, try the name of my village, which as mentioned elsewhere appears on the nameboard in upper case like this:

EGLWYSWRW