- hard to understand; recondite; esoteric: abstruse theories.
- Obsolete. secret; hidden.
- not easy to understand; recondite; esoteric
1590s, from Middle French abstrus (16c.) or directly from Latin abstrusus “hidden, concealed, secret,” past participle of abstrudere “conceal,” literally “to thrust away,” from ab- “away” (see ab-) + trudere “to thrust, push” (see extrusion). Related: Abstrusely; abstruseness.