The story
- Latin · derived fromimpenetrābilis
- Middle French · derived fromimpenetrable
- Middle English · inherited frominpenetrabel
- English todayimpenetrable
From Middle English inpenetrabel, inpenetrabyle, from Middle French impenetrable or directly from its etymon, Latin impenetrābilis. By surface analysis, im- + penetrable.
Etymology from Wiktionary, CC BY-SA 4.0.