Exercise

Any activity designed to develop or hone a skill or ability.

"The teacher told us that the next exercise is to write an essay."

Activity intended to improve physical, or sometimes mental, strength and fitness.

"I do crosswords for mental exercise."

A setting in action or practicing; employment in the proper mode of activity; exertion; application; use.

"The law guarantees us the free exercise of our rights."

The performance of an office, ceremony, or duty.

"I assisted the ailing vicar in the exercise of his parish duties."

To exert for the sake of training or improvement; to practice in order to develop.

"to exercise troops or horses;  to exercise one's brain with a puzzle"

To perform physical activity for health or training.

"I exercise at the gym every day."

To use (a right, an option, etc.); to put into practice.

"She is going to exercise her right to vote."

(now often in passive) To occupy the attention and effort of; to task; to tax, especially in a painful or vexatious manner; harass; to vex; to worry or make anxious.

"exercised with pain"