noun

1. 1. authorization or sanction, as by a superior or the law
   2. justification or reasonable grounds for some act, course, statement, or belief
2. something that serves as an assurance, or guarantee, of some event or result
3. a writing serving as authorization or certification for something; specif.,
   1. authorization in writing for the payment or receipt of money
   2. a short-term note issued by a municipality or other governmental agency, usually in anticipation of tax revenues
   3. an option issued by a company granting the holder the right to buy certain securities, generally common stock, at a specified price and usually for a limited time
   4. Law a writ or order authorizing an officer to make an arrest, seizure, or search, or perform some other designated act
   5. Mil. the certificate of appointment to the grade of warrant officer

Etymology: ME warant < NormFr (OFr garant), a warrant < Frank *warand < prp. of *warjan; akin to OE werian, to guard, defend: see weir

transitive verb

1. 1. to give (someone) authorization or sanction to do something
   2. to authorize (the doing of something)
2. to serve as justification or reasonable grounds for (an act, belief, etc.) a remark that did not warrant such anger
3. to give formal assurance, or guarantee, to (someone) or for (something); specif.,
   1. to guarantee the quality, quantity, condition, etc. of (goods) to the purchaser
   2. to guarantee to (the purchaser) that goods sold are as represented
   3. to guarantee to (the purchaser) the title of goods purchased; assure of indemnification against loss
   4. Law to guarantee the title of granted property to (the grantee)
4. Informal to state with confidence; affirm emphatically I warrant they'll be late