a flag flown on a ship to show which country it belongs to （表明国籍的）舰旗，船旗 the White Ensign (= the flag of the British Navy) 英国海军旗
an officer of low rank in the US navy （美国）海军少尉 Ensign Marshall 马歇尔海军少尉
Word Originlate Middle English: from Old French enseigne, from Latin insignia ‘signs of office’, neuter of insignis ‘distinguished (as if by a mark)’, from in- ‘towards’ + signum ‘sign’.