WordNet records no synonym and no antonym for withdrawer. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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.
an authority who withdraws permission
an individualist who withdraws from social interaction
a drug addict who is discontinuing the use of narcotics
a contestant who withdraws from competition
a student who withdraws from the educational institution in which he or she was enrolled
a depositor who withdraws funds previously deposited
Synonyms, antonyms and the broader and narrower relations for withdrawer come from Princeton University’s WordNet. Full sources and licences.