noun

• (countable) Any activity designed to develop or hone a skill or ability.
  "The teacher told us that the next exercise is to write an essay."
• (countable, uncountable) Activity intended to improve physical, or sometimes mental, strength and fitness.
  "Swimming is good exercise."
• (obsolete) That which gives practice; a trial; a test.
  "But patience is more oft the exerciſe / Of Saints, the trial of thir fortitude,"

verb

• (intransitive) To perform physical activity for health or training.
  "I exercise at the gym every day."
• (transitive) To use (a right, an option, etc.); to put into practice.
  "The tenant exercised his option to renew the tenancy."
• (now often passive voice) 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"
• (obsolete) To set in action; to cause to act, move, or make exertion; to give employment to.
  "And herein doe I exercise my selfe to haue alwayes a conscience void of offence toward God, and toward men."