WordNet records no synonym and no antonym for exceedance. 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.
(geology) the probability that an earthquake will generate a level of ground motion that exceeds a specified reference level during a given exposure time
“the concept of exceedance can be applied to any type of environmental risk modeling”
Synonyms, antonyms and the broader and narrower relations for exceedance come from Princeton University’s WordNet. Full sources and licences.