I just have to share with you this site I found today.  It’s a list of Welsh place names and their meanings. http://www.domesdaymaps.com/Welsh+Place+Names+Index.htm

Just some highlights:

BANGOR (Gwy) Bangor (1291). Earliest Welsh Record: Benchoer moer in Britannia (634). Meaning:from WELSH bangor ‘strong plaited rod in a fence’. The original monastic cell was either made of wattle or surrounded by a plaited fence.

BEDDGELERT (Gwy) Bedkelerd (1269). Earliest Record: Bekelert (1258). Meaning: from WELSHbedd ‘grave’ and a (probably Irish) personal name Celert or Cilert. Bethgelert, the 16th century spelling, is the first time the name appears to be linked with Llywelyn’s famous hound, Gelert(canine babysitter extraordinaire). The commemorative stone was erected by the enterprising landlord of the Royal Goat Hotel, David Prichard, in the 18th century to reinforce the legend.

CAREW (Dyf) Carew Meaning: possibly from WELSH carw ‘stag’. The Norman castle was rebuilt c. 1300.  (I discussed the meaning elsewhere on my blog:  http://www.sarahwoodbury.com/better-know-a-castle-carew/

DEE / DYFRDWY (Riv) Dee (1043) / Deverdoe (10th century). Earliest Record: Deova (in Greek) (150). Earliest Welsh Record: Dubr Duiu (c. 1214). Meaning: from BRITISH deva (related to the word divine) ‘the goddess’, thus ‘holy river’. In WELSH dwfr ‘water, river’ and Dee.

STRATA FLORIDA (Dyf) Strata Florida Meaning: a Latin form of WELSH ystrad ‘vale’ and fflur‘flowers’. The Abbey was founded in 1164.

SNOWDON / YR WYDDFA (Gwy) Snaudon (1284) / Yr Wyddfa Earliest Record: Snawdune (1095).Meaning: OE snaw ‘snow’ and dun ‘hill’. Welsh Meaning: from WELSH Y gwyddfa ‘the cairn, tumulus’;Eryri, from eryr ‘eagle’ refers to the mountains in general.