significance has 4 distinct synonyms spread across 2 of its 3 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 insignificance.
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.
the quality of being significant
“do not underestimate the significance of nuclear power”
Synonyms, antonyms and the broader and narrower relations for significance come from Princeton University’s WordNet. Full sources and licences.
a meaning that is not expressly stated but can be inferred
“the significance of his remark became clear only later”
the message that is intended or expressed or signified
“what is the meaning of this sentence”