Brythonic
Concise Oxford English Dictionary © 2008 Oxford University Press:
Brythonic /brɪˈθɒnɪk/ (also Brittonic)
▶noun the southern group of Celtic languages, consisting of Welsh, Cornish, and Breton. Compare with Goidelic. ▶adjective denoting or relating to Brythonic.
'Brythonic' also found in these Oxford entries:

