regular has 6 distinct synonyms spread across 6 of its 17 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 irregular.
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.
in accordance with fixed order or procedure or principle
“his regular calls on his customers”
(used of the military) belonging to or engaged in by legitimate army forces
“the regular army”
(of solids) having clear dimensions that can be measured; volume can be determined with a suitable geometric formula
not constipated
5 of the 17 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for regular.
Synonyms, antonyms and the broader and narrower relations for regular come from Princeton University’s WordNet. Full sources and licences.