execution has 12 distinct synonyms spread across 7 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. 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.
putting a condemned person to death
the act of performing; of doing something successfully; using knowledge as distinguished from merely possessing it
“they criticised his performance as mayor”
(computer science) the process of carrying out an instruction by a computer
(law) the completion of a legal instrument (such as a contract or deed) by signing it (and perhaps sealing and delivering it) so that it becomes legally binding and enforceable
a routine court order that attempts to enforce the judgment that has been granted to a plaintiff by authorizing a sheriff to carry it out
the act of accomplishing some aim or executing some order
“the agency was created for the implementation of the policy”
unlawful premeditated killing of a human being by a human being
Synonyms, antonyms and the broader and narrower relations for execution come from Princeton University’s WordNet. Full sources and licences.