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adjacent [adjacent 词源字典]: adjacent: [15] Adjacent and adjective come from the same source, the Latin verb jacere ‘throw’. The intransitive form of this, jacēre, literally ‘be thrown down’, was used for ‘lie’. With the addition of the prefix ad-, here in the sense ‘near to’, was created adjacēre, ‘lie near’. Its present participial stem, adjacent-, passed, perhaps via French, into English.

The ordinary Latin transitive verb jacere, meanwhile, was transformed into adjicere by the addition of the prefix ad-; it meant literally ‘throw to’, and hence ‘add’ or ‘attribute’, and from its past participial stem, adject-, was formed the adjective adjectīvus. This was used in the phrase nomen adjectīvus ‘attributive noun’, which was a direct translation of Greek ónoma épithetos.

And when it first appeared in English (in the 14th century, via Old French adjectif) it was in noun adjective, which remained the technical term for ‘adjective’ into the 19th century. Adjective was not used as a noun in its own right until the early 16th century.
=> adjective, easy, reject[adjacent etymology, adjacent origin, 英语词源]
adjacent (adj.): early 15c., from Latin adiacentem (nominative adiacens) "lying at," present participle of adiacere "lie at, border upon, lie near," from ad- "to" (see ad-) + iacere "to lie, rest," literally "to throw" (see jet (v.)), with notion of "to cast (oneself) down."
circumjacent (adj.): late 15c., from Latin circumiacens, present participle of circumiacere "to border upon, to lie round about, enjoin," from circum- "around" (see circum-) + iacere "to throw, cast, hurl" (see jet (v.)). Related: Circumjacence; circumjacency.
hic jacet: Latin, hic iacet, "here lies," commonly the first words of Latin epitaphs; from demonstrative pronominal adjective of place hic "here" + iacet "it lies," from iacere "to lie, rest," related to iacere "to throw" (see jet (v.)).
interjacent (adj.): 1590s, from Latin interiacentem (nominative interiacens) "lying between," present participle of interiacere "to lie between," from inter- (see inter-) + iacere (see jet (v.)).
subjacent (adj.): 1590s, from Latin subiacentem (nominative subiacens) "lying beneath," present participle of subiacere "to lie underneath, lie near, adjoin," from sub- "under," also "close to" (see sub-) + iacere "to throw" (see jet (v.)).
adjacently: "So as to be adjacent; contiguously", Early 19th cent. From adjacent + -ly.