Celticist
[ kel-tuh-sist, sel- ]
/ ˈkɛl tə sɪst, ˈsɛl- /
noun
an expert in Celtic languages or culture.
Also
Celt·ist
[kel-tist, sel-] /ˈkɛl tɪst, ˈsɛl-/,
Kelt·i·cist
[kel-tuh-sist] /ˈkɛl tə sɪst/.