indulgence has 11 distinct synonyms spread across 4 of its 5 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.
an inability to resist the gratification of whims and desires
a disposition to yield to the wishes of someone
“too much indulgence spoils a child”
the act of indulging or gratifying a desire
foolish or senseless behavior
the remission by the pope of the temporal punishment in purgatory that is still due for sins even after absolution
“in the Middle Ages the unrestricted sale of indulgences by pardoners became a widespread abuse”
Synonyms, antonyms and the broader and narrower relations for indulgence come from Princeton University’s WordNet. Full sources and licences.