deduction has 9 distinct synonyms spread across 6 of its 6 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.
a reduction in the gross amount on which a tax is calculated; reduces taxes by the percentage fixed for the taxpayer's income bracket
something that is inferred (deduced or entailed or implied)
“his resignation had political implications”
reasoning from the general to the particular (or from cause to effect)
the act of subtracting (removing a part from the whole)
“he complained about the subtraction of money from their paychecks”
the act of reducing the selling price of merchandise
Synonyms, antonyms and the broader and narrower relations for deduction come from Princeton University’s WordNet. Full sources and licences.