flowage has 1 distinct synonym spread across 1 of its 3 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.
gradual internal motion or deformation of a solid body (as by heat)
“rock fracture and rock flowage are different types of geological deformation”
a body of water that has been created by deliberately flooding an area
“many campsites were located near the flowage”
Synonyms, antonyms and the broader and narrower relations for flowage come from Princeton University’s WordNet. Full sources and licences.