Do you know ghouls from goblins and ghosts?
Old English undergan "undermine," from under + gan (see go). Cf. Middle Dutch ondergaen, Old High German untarkun, German untergehen, Danish undergaa. Sense of "submit to, endure" is attested from c.1300. Meaning "to pass through" (an alteration, etc.) is attested from 1630s. Related: Undergone; underwent.