WordNet records no synonym and no antonym for equal temperament. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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 division of the scale based on an octave that is divided into twelve exactly equal semitones
“equal temperament is the system commonly used in keyboard instruments”
Synonyms, antonyms and the broader and narrower relations for equal temperament come from Princeton University’s WordNet. Full sources and licences.