lieutenant

noun

1. Military.
   1. first lieutenant.
   2. second lieutenant.
2. U.S. Navy. a commissioned officer ranking between lieutenant junior grade and lieutenant commander.
3. a person who holds an office, civil or military, in subordination to a superior for whom he or she acts: If he can’t attend, he will send his lieutenant.

noun

1. a military officer holding commissioned rank immediately junior to a captain
2. a naval officer holding commissioned rank immediately junior to a lieutenant commander
3. US an officer in a police or fire department ranking immediately junior to a captain
4. a person who holds an office in subordination to or in place of a superior

n.late 14c., “one who takes the place of another,” from Old French lieu tenant “substitute, deputy,” literally “placeholder,” from lieu “place” (see lieu) + tenant, present participle of tenir “to hold” (see tenant). The notion is of a “substitute” for higher authority. Specific military sense of “officer next in rank to a captain” is from 1570s. Pronunciation with lef- is common in Britain, and spellings to reflect it date back to 14c., but the origin of this is a mystery (OED rejects suggestion that it comes from old confusion of -u- and -v-).