ponderable has 1 distinct synonym spread across 1 of its 2 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 imponderable.
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.
capable of being weighed or considered
“something ponderable from the outer world--something of which we can say that its weight is so and so”
capable of being thought about
“space flight to other galaxies becomes more cogitable”
Synonyms, antonyms and the broader and narrower relations for ponderable come from Princeton University’s WordNet. Full sources and licences.