expense has 4 distinct synonyms spread across 2 of its 4 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
amounts paid for goods and services that may be currently tax deductible (as opposed to capital expenditures)
a detriment or sacrifice
“at the expense of”
money spent to perform work and usually reimbursed by an employer
“he kept a careful record of his expenses at the meeting”
reduce the estimated value of something
“For tax purposes you can write off the laser printer”
Synonyms, antonyms and the broader and narrower relations for expense come from Princeton University’s WordNet. Full sources and licences.