1630s, "touching the feelings intensely," figurative present-participle adjective from penetrate (v.). It was used earlier in a literal sense (early 15c.). The sense of "acute, discerning, quick to discover or recognize" is from 1670s. An earlier adjective was penetrative (late 14c., penetratif), in reference to medicines, from Medieval Latin penetrativus. Related: Penetratingly.