impressionable has 2 distinct synonyms spread across 1 of its 1 sense. 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 unimpressionable.
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.
easily impressed or influenced
“an impressionable youngster”
Synonyms, antonyms and the broader and narrower relations for impressionable come from Princeton University’s WordNet. Full sources and licences.