increase has 5 distinct synonyms spread across 4 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 decrease.
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.
a quantity that is added
“there was an addition to property taxes this year”
a change resulting in an increase
“the increase is scheduled for next month”
Synonyms, antonyms and the broader and narrower relations for increase come from Princeton University’s WordNet. Full sources and licences.
a process of becoming larger or longer or more numerous or more important
“the increase in unemployment”
the amount by which something increases
“they proposed an increase of 15 percent in the fare”
the act of increasing something
“he gave me an increase in salary”