Erse vs Celtic language

Erse and Celtic language both are nouns.

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

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

Erse: any of several related languages of the Celts in Ireland and Scotland
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 Erse include Celtic.

Erse (noun)	Celtic language (noun)
any of several related languages of the Celts in Ireland and Scotland	a branch of the Indo-European languages that (judging from inscriptions and place names) was spread widely over Europe in the pre-Christian era