IPA: /ˈdrɪlˌmɑːstər/
KK: /ˈdrɪlˌmæstər/
A person who teaches and trains others, especially in a strict or disciplined way, often in a military context.
The drillmaster led the recruits through their training exercises with precision and authority.
Drillmaster → It is formed from "drill" (from Middle English *drillen*, meaning to bore or to make a hole) and "master" (from Old English *maegester*, meaning one who has control or authority). A drillmaster is someone who has authority in teaching or training, particularly in a disciplined manner.
Think of someone who 'bore' or 'made a hole' ('drill') in a disciplined way, guiding others as a 'master' — that's what a drillmaster does.
No commonly confused words.