absorption has 7 distinct synonyms spread across 5 of its 6 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.
(chemistry) a process in which one substance permeates another; a fluid permeates or is dissolved by a liquid or solid
(physics) the process in which incident radiated energy is retained without reflection or transmission on passing through a medium
“the absorption of photons by atoms or molecules”
the social process of absorbing one cultural group into harmony with another
the process of absorbing nutrients into the body after digestion
complete attention; intense mental effort
the mental state of being preoccupied by something
Synonyms, antonyms and the broader and narrower relations for absorption come from Princeton University’s WordNet. Full sources and licences.