abstruse (adj.)

word-forming element meaning "away, from, from off, down," denoting disjunction, separation, departure; from Latin ab (prep.) "off, away from" in reference to space or distance, also of time, from PIE root *apo- "off, away" (also the source of Greek apo "off, away from, from," Sanskrit apa "away from," Gothic af, English of, off; see apo-).

The Latin word also denoted "agency by; source, origin; relation to, in consequence of." Since classical times usually reduced to a- before -m-, -p-, or -v-; typically abs- before -c-, -q-, or -t-.

Old English þreat "crowd, troop," also "oppression, coercion, menace," related to þreotan "to trouble, weary," from Proto-Germanic *thrautam (source also of Dutch verdrieten, German verdrießen "to vex"), from PIE *treud- "to push, press squeeze" (source also of Latin trudere "to press, thrust," Old Church Slavonic trudu "oppression," Middle Irish trott "quarrel, conflict," Middle Welsh cythrud "torture, torment, afflict"). Sense of "conditional declaration of hostile intention" was in Old English.