back has 29 distinct synonyms spread across 13 of its 28 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. Its 4 recorded opposites are advance, front, veer, ahead.
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.
cause to travel backward
“back the car into the parking spot”
support financial backing for
“back this enterprise”
strengthen by providing with a back or backing
the side that goes last or is not normally seen
“he wrote the date on the back of the photograph”
related to or located at the back
“the back yard”
5 of the 28 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for back.
Synonyms, antonyms and the broader and narrower relations for back come from Princeton University’s WordNet. Full sources and licences.
(football) a person who plays in the backfield
the series of vertebrae forming the axis of the skeleton and protecting the spinal cord
“the fall broke his back”
the protective covering on the front, back, and spine of a book
“the book had a leather binding”
the part of a garment that covers the back of your body
“they pinned a `kick me' sign on his back”
a support that you can lean against while sitting
“the back of the dental chair was adjustable”
(American football) the position of a player on a football team who is stationed behind the line of scrimmage