ejercitar
/exeɾθiˈtaɾ/ · B2 · verb
to exercise, practice
🏋️ ejercitar = ejército (army) + -ar: drill like an army
From Latin exercitare, to train often. Ejército (army) has the same root: a body of trained men. Ejercicio is an exercise, so ejercitar means to keep practising a skill or a muscle until it is drilled in.