average has 11 distinct synonyms spread across 9 of its 12 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.
approximating the statistical norm or average or expected value
“the average income in New England is below that of the nation”
relating to or constituting the most frequent value in a distribution
“the modal age at which American novelists reach their peak is 30”
relating to or constituting the middle value of an ordered set of values (or the average of the middle two in a set with an even number of values)
“the median value of 17, 20, and 36 is 20”
amount to or come to an average, without loss or gain
“The number of hours I work per work averages out to 40”
achieve or reach on average
“He averaged a C”
Synonyms, antonyms and the broader and narrower relations for average come from Princeton University’s WordNet. Full sources and licences.
(sports) the ratio of successful performances to opportunities
an intermediate scale value regarded as normal or usual
“he is about average in height”