【Practice】 ,  【exercise】 ,  【drill】  are comparable when they mean, as verbs, to perform or cause one to perform an act or series of acts repeatedly and, as nouns, such repeated activity or exertion.

【Practice】 fundamentally implies doing, especially doing habitually or regularly, often in contrast to thinking, believing, and professing or to theory and precept.

【Practice】 also implies a doing over and over again of certain acts for the sake of acquiring proficiency, dexterity, or skill or in the hope of attaining perfection.

【Exercise】 fundamentally implies a keeping busy or a setting to work; it usually presupposes the possession of a power or of powers which can be developed or strengthened by activity, especially repeated activity, or can be manifested only in 【practice】 .

Like 【practice】 , 【exercise】  may be used also to imply acts performed repeatedly for the sake of an ulterior end, but  【exercise】 refers especially to those directed to the attainment of health or vigor (as of body or mind).

【Drill】 fundamentally connotes an intention to fix physical or mental habits as deeply as though they were bored in by the use of a 【drill】 ; the term stresses repetition (as of military evolutions, of word pronunciations, or of grammatical rules) as a means of training and disciplining the body or mind or of forming correct habits.