List of English words of Brittonic origin
The number of English words known to be derived from the ancient Brittonic language is small – in fact, it is lower than the number of Gaulish words found in the English language, most of which were borrowed in from French. However, this is to be expected, given the socio-historical relationship between Old English and Brittonic; the influence of the Brittonic language has been more prominent in other areas such as syntax. However, it is possible that many British words have been obscured by their close similarity to Germanic words which are perceived to offer a more likely etymology (eg "belly": considered to be from OE bylg, but could easily be from AB *belgā), and also that some of them have been misidentified as Gaulish via French which are simply unattested until after the Norman invasion. This list also leaves out words of Celtic origin thought to have been borrowed into English from Welsh (e.g. "coracle"), Gaelic (e.g. "whiskey, to keen, bog, bother, hubbub, glen, clan"), Cornish (e.g. "scad, vug, wrasse", possibly gull"), Breton (dolmen, menhir, bijou, all through French), Gaulish by means of French or Latin (league, carpenter, budget, car, etc. possibly beak, bran, barrel, branch, bin, bound, gallon, bound, moat, piece, etc.), unknown Brythonic Celtic (e.g. gull), or unknown Celtic in general (e.g. down).
- possibly from Brittonic *basc(i)-etto-, meaning "little wicker thing".
- from Brittonic *brocco-, meaning "badger".
- from Brittonic *cumbos-/ā-, meaning "valley".
- possibly from a Brittonic root *da-. 
- yan, tan, tethera etc.
- from Brittonic *oinā, deŭai, tisrīs etc., although heavily corrupted by the nature of the survival.
This list is not exhaustive.
- Tristram, Hildegaard 2007: "Why Don't the English Speak Welsh" http://www.hildegard.tristram.de/media/tristram_manchester_30-07-07.pdf