abstruse
— Adjective
– English
~ difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge; "the professor's lectures were so abstruse that students tended to avoid them"; "a deep metaphysical theory"; "some recondite problem in historiography"
abstrusely
— Adverb
– English
~ in a manner difficult to understand; "the professor's abstrusely reasoned theories were wasted on his students"