secondary has 7 distinct synonyms spread across 2 of its 7 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 primary.
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.
being of second rank or importance or value; not direct or immediate
“the stone will be hauled to a secondary crusher”
the defensive football players who line up behind the linemen
coil such that current is induced in it by passing a current through the primary coil
3 of the 7 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 secondary.
Synonyms, antonyms and the broader and narrower relations for secondary come from Princeton University’s WordNet. Full sources and licences.