From Longman Dictionary of Contemporary Englishfirst lieutenantˌfirst lieuˈtenant noun [countable] PMa middle rank in the US army, Marines, or Air Force, or someone who has this rank
Examples from the Corpus
first lieutenant• This was Mark Rhoads, a first lieutenant in the Signal Corps who had been carefully selected for the assignment.• A first lieutenant was the highest-ranking officer at the scene.• The yeoman informed him that the public information officer was also the base first lieutenant and had important business else-where.• He was promoted first lieutenant in November 1914 and captain nine months later.• And Graham Gooch's first lieutenant Stewart, the Surrey skipper, will be a key witness at a committee of inquiry.• The first lieutenant also refused and also went below.• We know that you have commanded a submarine and the Lieutenant-Commander was your first lieutenant. 