absence has 1 distinct synonym spread across 1 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. Its one recorded opposite is presence.
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 state of being absent
“he was surprised by the absence of any explanation”
failure to be present
the time interval during which something or somebody is away
“he visited during my absence”
the occurrence of an abrupt, transient loss or impairment of consciousness (which is not subsequently remembered), sometimes with light twitching, fluttering eyelids, etc.; common in petit mal epilepsy
Synonyms, antonyms and the broader and narrower relations for absence come from Princeton University’s WordNet. Full sources and licences.