The Collaborative International Dictionary
Celticize
Celticize \Celt"i*cize`\, v. t. To render Celtic; to assimilate to the Celts.
Wiktionary
celticize
vb. (context transitive English) To render Celtic; to assimilate into the Celts.
Usage examples of "celticize".
But similar things, historically and linguistically undocumented, though conjectured by archaeology, must have occurred in the course of the celticizing of Britain.