/ lefˈtenənt; NAmE luːˈt-/ noun ( abbr. Lieut. , Lt )
1.
an officer of middle rank in the army, navy, or air force :
Lieutenant Paul Fisher
—see also flight lieutenant , second lieutenant , sub lieutenant
2.
(in compounds) an officer just below the rank mentioned :
a lieutenant colonel
3.
(in the US) a police officer of fairly high rank
4.
a person who helps sb who is above them in rank or who performs their duties when that person is unable to
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WORD ORIGIN
late Middle English : from Old French (see lieu , tenant ).