Words for doctor in Celtic languages.

Irish (Gaeilge)	dochtúir [d̪ˠɔxˈt̪ˠuːɾʲ / ˈd̪ˠʌxt̪ˠuɾʲ] = doctor
Scottish Gaelic (Gàidhlig)	dotair [dɔhdɛrʲ] = doctor, surgeon, physician
Manx (Gaelg)	doghtoor = doctor

Etymology: from the Latin doctor (teacher, instructor), from doceō (teach), from the Proto-Italic *dokeō (tell, inform, teach, instruct), from the Proto-Indo-European *deḱ- (to take) [source].

Sources: Wiktionary, Am Faclair Beag, teanglann.ie, Dictionary of the Irish Language On-Line Manx Dictionary

Proto-Celtic	*lī(φ)agi- = doctor
Old Irish (Goídelc)	líaig = leech, doctor, physician
Irish (Gaeilge)	lia = healer, physician
Scottish Gaelic (Gàidhlig)	lèigh [ʎeː] = physician, surgeon lighiche [ʎi.ɪçə] = healer, physician, surgeon
Manx (Gaelg)	(fer/ben) lhee = (male/female) doctor, physician

Etymology: from the Proto-Indo-European lēg(‘)- (doctor), the same root as the English word leech [source].

Sources: Wiktionary, Proto-Celtic English Word List, Am Faclair Beag, teanglann.ie, Dictionary of the Irish Language On-Line Manx Dictionary

Proto=Brythonic	*meðïg = doctor
Welsh (Cymraeg)	meddyg [ˈmɛðɪɡ / ˈmeːðɪɡ] = doctor
Cornish (Kernewek)	medhek [mɛðɛk / ‘mɛðɐk] = doctor, physician
Breton (Brezhoneg)	mezeg = doctor

Etymology: from the Latin medicus (doctor), from medeor (I heal, cure, remedy), from the Proto-Italic *medēōr (to heal), from the Proto-Indo-European *med- (to measure, give advice, heal) [source].

Words marked with a * are reconstructions.

Sources: Wiktionary, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionnaire Favereau