automatic has 9 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. Its one recorded opposite is manual.
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.
operating with minimal human intervention; independent of external control
“automatic transmission”
resembling the unthinking functioning of a machine
“an automatic `thank you'”
a pistol that will keep firing until the ammunition is gone or the trigger is released
Synonyms, antonyms and the broader and narrower relations for automatic come from Princeton University’s WordNet. Full sources and licences.