officer has 5 distinct synonyms spread across 4 of its 5 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
any person in the armed services who holds a position of authority or command
“an officer is responsible for the lives of his men”
Synonyms, antonyms and the broader and narrower relations for officer come from Princeton University’s WordNet. Full sources and licences.
someone who is appointed or elected to an office and who holds a position of trust
“he is an officer of the court”
a person authorized to serve in a position of authority on a vessel
“he is the officer in charge of the ship's engines”