abstruse

adj

1. (formal)Difficult to comprehend or understand; obscure.

   “Some time the good makithe an ile end⸝ ãd the ile a godd. In this opiniõ⸝ and in ſcrutable miſterie be werithe all his wittes⸝ and at the end of his cogitacions⸝ fyndithe more abſtruſe⸝ and doutfull obiections thẽ at the beginning⸝ […]”

   “Be leſs abſtruſe, my riddling days are paſt.”

   “Thoſe propoſitions relating to the Moon's motion, which are demonſtrated in the Principia [by Isaac Newton], do generally depend on calculations very intricate and abſtruſe, the truth of which is not eaſily examined, even by thoſe that are moſt skilful; […]”

   “The beſt VVay to learn any Science, is to begin vvith a regular Syſtem, or a ſhort and plain Scheme of that Science, vvell dravvn up into a narrovv Compaſs, omitting the deeper and more abſtruſe Parts of it, and that alſo under the Conduct and Inſtruction of ſome ſkilful Teacher.”

   “'Tis certain, that the eaſy and obvious Philoſophy vvill always, vvith the Generality of Mankind, have the Preference to the accurate and abſtruſe; and by many vvill be recommended, not only as more agreeable, but more uſeful than the other.”

2. (formal, obsolete)Concealed or hidden; secret.

   “O vvho is he that could carrie nevves to our olde father, that thou vvert but aliue, although thou vvert hidden in the moſt abſtruſe dungeons of Barbarie; for his riches, my brothers and mine vvould fetch thee from thence.”

   “[T]he abſtruſeſt Things / VVhich in the Mindes dark Temper neſtling ly, / By you expoſed are to every Eye.”

   “Mean while th’ Eternal eye, whoſe ſight diſcernes / Abſtruſeſt thoughts, from forth his holy Mount / And from within the golden Lamps that burne / Nightly before him, ſaw without their light / Rebellion riſing, ſaw in whom, how ſpred / Among the ſons of Morn, what multitudes / Were banded to oppoſe his high Decree; […]”