magical formula, 1690s, from Latin (Q. Serenus Sammonicus, 2c.), from Late Greek Abraxas, cabalistic or gnostic name for the supreme god, and thus a word of power. It was written out in a triangle shape and worn around the neck to ward off sickness, etc. Another magical word, from a mid-15c. writing, was ananizapta.

1690s, "unfathomable, unsearchably deep, like an abyss," from abyss + -al (1). Since 19c. mainly "inhabiting or belonging to the depths of the ocean" (used especially of the zone of ocean water below 300 fathoms), though in 19c. abysmal was more common in oceanography.

1690s, from Medieval Latin accentuationem (nominative accentuatio) "intoning, chanting," noun of action from past-participle stem of accentuare "to accent," from Latin accentus "song added to speech," from ad "to" (see ad-) + cantus "a singing," past participle of canere "to sing" (from PIE root *kan- "to sing").

"collected into a mass or quantity," 1690s, past-participle adjective from accumulate (v.). The earlier adjective was accumulate (1530s, from Latin past participle accumulatus).

1690s, from acid (adj.); originally loosely applied to any substance having a sour taste like vinegar, in modern chemistry it was gradually given more precise definitions from early 18c. and is given to many compounds which do not have such a taste.

The slang meaning "LSD-25" first recorded 1966 (see LSD).

When I was on acid I would see things that looked like beams of light, and I would hear things that sounded an awful lot like car horns. [Mitch Hedberg, 1968-2005, U.S. stand-up comic]

Acid rock (type performed or received by people using LSD) is also from 1966; acid house dance music style is 1988, probably from acid in the hallucinogenic sense + house "dance club DJ music style."

"disposed to yield, submissive," 1690s (implied in acquiescently), from Latin acquiescentem (nominative acquiescens), present participle of acquiescere "become quiet, remain at rest" (see acquiesce).

1690s, "tending to be added," from Late Latin additivus "added, annexed," past-participle adjective from Latin addere "add to, join, attach" (see addition). Alternative addititious "additive, additional" (1748) is from Latin additicius "additional."

1690s, "completely skilled, well-versed," from Latin adeptus "having reached or attained," past participle of adipisci "to come up with, arrive at," figuratively "to attain to, acquire," from ad "to" (see ad-) + apisci "to grasp, attain" (related to aptus "fitted," from PIE root *ap- (1) "to take, reach," for which see apt). Related: Adeptly; adeptness.

1690s, "action of adjudging," from French adjudication or directly from Late Latin adiudicationem (nominative adiudicatio), noun of action from past-participle stem of adiudicare "grant or award as a judge" (see adjudge). By 1782 as "a judicial settlement."

"long narrow passage for admitting air," 1690s, from air (n.1) + shaft (n.2).