Entry 1 sense Webster, 1913 Impassable /ĭmˌ-păs'-əb-əl/ · Im·pass·a·ble · IPA /ˌɪmpˈæsəbəl/ 01 a. Incapable of being passed; not admitting a passage; as, an impassable road, mountain, or gulf. 1. Incapable of being passed; not admitting a passage; as, an impassable road, mountain, or gulf.