IPA: /ˈkoʊtʃər/
KK: /ˈkoʊtʃər/
A person who trains or instructs others in a particular skill or sport.
The coacher helped the team improve their performance before the big game.
Coacher is derived from the word 'coach' (from Old French *coche*, meaning a large, horse-drawn vehicle) and the suffix '-er' (meaning a person who). A coacher is a person who drives or operates a coach, or metaphorically, someone who trains or instructs others.
Think of a 'coach' as a person who guides or trains others, and the '-er' indicates that this person is actively involved in that role.