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cave [cave 词源字典]: cave: There are two English words cave which, despite their apparent similarity, are probably unrelated. The earlier, ‘underground chamber’ [13], comes via Old French cave from Latin cavea, a nominal use of the adjective cavus ‘hollow’ (source also of cavern [14], via Old French caverne or Latin caverna, and of cavity [16], from the late Latin derivative cavitās).

The verb cave [18], however, as in ‘cave in’, seems to come from an earlier dialectal calve ‘collapse, fall in’, once widespread in the eastern counties of England; it has been speculated that this was borrowed from a Low German source, such as Flemish inkalven. It has subsequently, of course, been much influenced by the noun cave.
=> cavern, cavity, decoy[cave etymology, cave origin, 英语词源]
apparent (adj.): late 14c., from Old French aparant "evident, obvious, visible," from Latin apparentem (nominative apparens) "visible, manifest," present participle of apparere (see appear). First attested in phrase heir apparent (see heir). Meaning "superficial" is c. 1400. Apparent magnitude in astronomy (how bright a heavenly body looks from earth, as opposed to absolute magnitude, which is how bright it really is) is attested from 1875.
heir (n.): c. 1300, from Anglo-French heir, Old French oir "heir, successor," from Latin heredem (nominative heres) "heir, heiress" (see heredity). Heir apparent (late 14c.) has the French order of noun-adjective, though it was not originally so written in English. It is the heir of one still alive whose right is clear. After death the heir apparent becomes the heir-at-law.
presumptive (adj.): "speculative," mid-15c., from French présomptif (15c.), from Medieval Latin presumptivus, from Late Latin praesumptivus, from Latin praesumpt- past participle stem of praesumere (see presume). The heir presumptive (1620s) is "presumed" to be the heir if the heir apparent is unavailable. Related: Presumptively.