Brythonic vs Celtic language

Brythonic and Celtic language both are nouns.

Word	Noun	Adjective	Verb	Adverb
Brythonic	Yes	No	No	No
Celtic language	Yes	No	No	No

As nouns, Celtic language is a hypernym of Brythonic; that is, Celtic language is a word with a broader meaning than Brythonic:

Brythonic: a southern group of Celtic languages
Celtic language: a branch of the Indo-European languages that (judging from inscriptions and place names) was spread widely over Europe in the pre-Christian era

Other hypernyms of Brythonic include Celtic.

Brythonic (noun)	Celtic language (noun)
a southern group of Celtic languages	a branch of the Indo-European languages that (judging from inscriptions and place names) was spread widely over Europe in the pre-Christian era