n.1 a deputy or substitute acting for a superior.
2 a an army officer next in rank below captain. b a naval officer next in rank below lieutenant commander.
3 US a police officer next in rank below captain.
Phrases and idioms:
lieutenant colonel (or commander or general) officers ranking next below colonel, commander, or general. lieutenant-governor the acting or deputy governor of a State, province, etc., under a governor or Governor-General. Lieutenant of the Tower the acting commandant of the Tower of London.
Derivatives:
lieutenancy n. (pl. -ies).
Etymology: ME f. OF (as LIEU, TENANT)