Abstruse
Abstruse ({not transcribed}) , adjective
[Latin abstrusus, past participle of abstrudere to thrust away, conceal; ab, abs + trudere to thrust; compare French abstrus. See Threat.]
1.
Concealed or hidden out of the way. [Obsolete]
The eternal eye whose sight discerns
Abstrusest thoughts.
2.
Remote from apprehension; difficult to be comprehended or understood; recondite; as, abstruse learning.
Profound and abstruse topics.