Meaning

adjective difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge

originPIE word *h₂epó Learned borrowing from Latin abstrūsus (“concealed, hidden; having been concealed”), an adjective use of the perfect passive participle of abstrūdō (“to conceal, hide; to push or thrust away”), from abs- (from ab- (prefix meaning ‘away; from; away from’)) + trūdō (“to push, shove; to thrust”) (ultimately from Proto-Indo-European *trewd- (“to push; to thrust”)). Cognates * Catalan…

Etymology from Wiktionary, CC BY-SA 3.0