ABSTRU'SE, adjective [Latin abstrusus, from abstrudo, to thrust away, to conceal; abs and trudo; Eng. to thrust.] Hid; concealed; hence, remote from apprehension; difficult to be comprehended or understood; opposed to what is obvious. [Not used of material objects.] Metaphysics is an abstruse science.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI