immaterial has 6 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 material.
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.
of no importance or relevance especially to a law case
“an objection that is immaterial after the fact”
Synonyms, antonyms and the broader and narrower relations for immaterial come from Princeton University’s WordNet. Full sources and licences.
not pertinent to the matter under consideration
“an issue extraneous to the debate”
(often followed by `to') lacking importance; not mattering one way or the other
“whether you choose to do it or not is a matter that is quite immaterial (or indifferent)”