overcast has 7 distinct synonyms spread across 5 of its 8 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 clear up.
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.
the state of the sky when it is covered by clouds
a long whipstitch or overhand stitch overlying an edge to prevent raveling
a cast that falls beyond the intended spot
sew with an overcast stitch from one section to the next
“overcast books”
filled or abounding with clouds
Synonyms, antonyms and the broader and narrower relations for overcast come from Princeton University’s WordNet. Full sources and licences.