Etymology
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Aden 

place in southern Arabia, ultimately from Akkadian edinnu "plain," which some think also is the root of Biblical Eden. The two place-names sometimes were treated as synonymous in English (Byron, Poe, etc.).

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adenine (n.)

crystalline base, 1885, coined by German physiologist/chemist Albrecht Kossel from Greek adēn "gland" (see adeno-) + chemical suffix -ine (2). So called because it was derived from the pancreas of an ox.

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adeno- 

scientific word-forming element meaning "gland," from Greek adēn "gland," which is perhaps from a suffixed form of PIE root *engw- "groin; internal organ" (source also of Latin inguen "groin"), but Beekes rejects all cognates and calls it isolated.

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adenoid (adj.)

1839, "gland-like," from medical Latin adenoideus, from Greek adenoeides, from adēn (genitive adēnos) "gland" (see adeno-) + eidos "form" (see -oid). Adenoids (n.) "adenoid growths" is attested by 1856.

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adenoidal (adj.)

1852, "gland-like, resembling a gland," from adenoid + -al (1). From 1919 as "having the appearance of one with adenoids."

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adept (adj.)

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.

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adept (n.)

"an expert, one who has attained knowledge," especially "one who is skilled in the secrets of an occult science," 1660s, from Latin adeptus (adj.) "having attained" (see adept (adj.)). The Latin adjective was used as a noun in this sense in Medieval Latin among alchemists. It implies natural and acquired ability, whereas expert implies more of experience and practice.

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adequacy (n.)

"condition of being proportionate or sufficient; a sufficiency for a particular purpose," 1794; see adequate + abstract noun suffix -cy. Adequateness is from 1670s.

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adequate (adj.)

1610s, "equal to what is needed or desired, sufficient," from Latin adaequatus "equalized," past participle of adaequare "to make equal to, to level with," from ad "to" (see ad-) + aequare "make level," from aequus "equal, even" (see equal (adj.)).

The sense is of being "equal to what is required." It shares duty with enough, depending on the subject. Somewhat disparaging use, "mediocre, just good enough," is by 1900. Related: Adequateness.

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adequately (adv.)

1620s; see adequate + -ly (2); originally a term in logic in reference to correspondence of ideas and objects and probably based on Latin use. Meaning "suitably" is recorded from 1680s.

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