schoolmaster vs head teacher

schoolmaster and head teacher both are nouns.

Word	Noun	Adjective	Verb	Adverb
schoolmaster	Yes	No	No	No
head teacher	Yes	No	No	No

As nouns, head teacher is a hypernym of schoolmaster; that is, head teacher is a word with a broader meaning than schoolmaster:

Other hypernyms of schoolmaster include adult male, man, head, principal, school principal.

schoolmaster (noun)	head teacher (noun)
food fish of warm Caribbean and Atlantic waters	the educator who has executive authority for a school
presiding officer of a school
any person (or institution) who acts as an educator