noun

• (countable) A controlled regimen of food and drink choices, as to gain or lose weight or otherwise influence health.
  "He's been on a diet since he found out that he has coronary atherosclerosis."
• (by extension) Any habitual intake or consumption.
  "He's been reading a steady diet of nonfiction for the last several years."

adj

• (of a food or beverage) Containing less fat, salt, sugar, or calories than normal, or claimed to have such.
  "diet soda"
• (informal, figurative) Having certain traits subtracted.
  "You folks reduce it to the bible only as being authoritative, impoverishing the faith. "Christianity Lite", diet Christianity for those who can't handle the Whole Meal."

verb

• (intransitive) To modify one's food and beverage intake so as to decrease or increase body weight or influence health.
  "I've been dieting for six months, and I've lost some weight."
• (transitive, dated) To regulate the food of (someone); to put on a diet.
  "they will diet themselves, feed and live alone."
• (obsolete) To eat; to take one's meals.
  "Let him[…]diet in such places, where there is good company of the nation, where he travelleth."
• (obsolete, transitive) To cause to take food; to feed.
  "But partly led to diet my revenge […]."

noun

• (usually capitalized as a proper noun) A council or assembly of leaders; a formal deliberative assembly.
  "the National Diet of Japan"
• (Scotland) A session of exams.
  "Normally the diet begins towards the end of April."
• (Scots law) A criminal proceeding in court.
• (Scotland) A clerical or ecclesiastical function in Scotland.
  "a diet of worship"