What's the noun for lieutenant? Here's the word you're looking for.
lieutenant
(military) The lowest commissionedofficer rank or ranks in many military forces.
(military, US) In the US Army, Air Force and Marines, second lieutenant is the rank below first lieutenant, which is below captain. Both ranks may be referred to as Lieutenant or as the complete forms of the ranks.
(military, US, navy) A naval officer whose rank is above that of ensign in the United States Navy and below that of a lieutenant commander. There are two ranks of lieutenant: lieutenant junior grade and lieutenant.
(military, US) A commissioned officer in the United States Coast Guard, Public Health Service, or National Atmospheric and Oceanic Administration whose rank is above that of ensign and below lieutenant commander. There are two ranks of lieutenant: lieutenant junior grade and lieutenant.