capacity has 5 distinct synonyms spread across 4 of its 9 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 incapacity.
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.
capability to perform or produce
“among his gifts is his capacity for true altruism”
the susceptibility of something to a particular treatment
“the capability of a metal to be fused”
the amount that can be contained
“the gas tank has a capacity of 12 gallons”
the maximum production possible
“the plant is working at 80 per cent capacity”
a specified function
“he was employed in the capacity of director”
(computer science) the amount of information (in bytes) that can be stored on a disk drive
“the capacity of a hard disk drive is usually expressed in megabytes”
an electrical phenomenon whereby an electric charge is stored
the power to learn or retain knowledge; in law, the ability to understand the facts and significance of your behavior
tolerance for alcohol
“he had drunk beyond his capacity”
Synonyms, antonyms and the broader and narrower relations for capacity come from Princeton University’s WordNet. Full sources and licences.