drill master vs drill instructor

drill master and drill instructor both are nouns.

Word	Noun	Adjective	Verb	Adverb
drill master	Yes	No	No	No
drill instructor	Yes	No	No	No

As nouns, drill master and drill instructor are synonyms defined as:

drill master and drill instructor: a noncommissioned officer who instructs recruits in military marching and discipline

drill master (noun)	drill instructor (noun)
a noncommissioned officer who instructs recruits in military marching and discipline	a noncommissioned officer who instructs recruits in military marching and discipline