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"
being or characterized by concepts or their formation; "conceptual discussions"; "the schizophrenic loses ability to abstract or do conceptual thinking"; "sex is a notional category, gender is a grammatical category"
the calculated use of violence (or threat of violence) against civilians in order to attain goals that are political or religious or ideological in nature; this is done through intimidation or coercion or instilling fear