hi, wordwind - welcome to the nuthouse!

I can think of a few off the cuff (or is that cwfff?)

dwr = water
swn = sound

(those two should have a 'to' or roof over the 'w' - like this letter's: û - but I can't seem to find that in the standard character sets...)

ffrwd = misty, damp (I think)
twr = tower
twll = hole
bwlch = gap (in hills etc), pass
hwn = that

Perhaps Rod and others will think of some more. What's your interest in Welsh words derived from?

Here's on online course in Welsh language.

http://www.cs.brown.edu/fun/welsh/home.html

Please, Mav, What's Welsh for "nuthouse?" ;) Thanks

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

We got a book this weekend written in Plattdeutsch ("low German"). It uses w as a vowel - and wait, that's not all! - the w is umlauted!

My ASp trumpeth me.

But I have not completely conviced myself that it is Plattdeutsch. We have neither of us given it more than the most cursory of looks so far. It was in the Plattdeutsch section but so were some other thangs that were definitely not Plattdeutsch (including some Middle English {or should I say Mittelenglische} tales in a Hoch Deutsch matrix).

Fwiw! So hôw cân I do that tw, my favoûrite wîtch?

and btw, 'to' is pr. something almost like 'tor', and means 'roof'... very direct language, Welsh!