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defalcate [defalcate 词源字典]: defalcate: [15] Defalcate comes from medieval Latin dēfalcāre ‘cut off’, a compound verb formed from the prefix dē- ‘off’ and falx ‘sickle’ (source of French faux ‘scythe’). At first it meant simply ‘deduct’ in English; the modern legal sense ‘embezzle’ did not develop until the 19th century.
[defalcate etymology, defalcate origin, 英语词源]
defalcation (n.): mid-15c., from Medieval Latin defalcationem (nominative defalcatio), noun of action from past participle stem of defalcare, from de- + Latin falx, falcem "sickle, scythe, pruning hook" (see falcate).
falcate (adj.): "hooked, curved like a scythe or sickle," 1801, from Latin falcatus "sickle-shaped, hooked, curved," from falcem (nominative falx) "sickle," which is of uncertain origin, perhaps a borrowing from a non-Latin Indo-European language of Italy. De Vaan lists cognates as Old Irish delg "thorn, pin," Welsh dala "sting," Lithuanian dilge "nettle," Old Norse dalkr "pin, spine, dagger," Old English delg "clasp." Related: Falcated; falcation; falciform (1766).
falchion (n.): "a broad sword, somewhat curved," c. 1300, fauchoun, from Old French fauchon "curved sword," from Vulgar Latin *falcionem, from diminutive of Latin falx "sickle" (see falcate). Partially re-Latinized in early Modern English.
falcon (n.): mid-13c., faucon, from Old French faucon "falcon" (12c.), from Late Latin falconem (nominative falco) "falcon" (source also of Old Spanish falcon, Portuguese falcão, Italian falcone, Old High German falcho, German Falke, Dutch valk), probably from Latin falx (genitive falcis) "curved blade, pruning hook, sickle, war-scythe" (see falcate); the bird said to be so called for the shape of its talons, legs, or beak, but also possibly from the shape of its spread wings.

The other theory is that the Latin bird name falx is of Germanic origin and means "gray bird" (from the source of fallow (adj.)), which is supported by the antiquity of the word in Germanic but opposed by those who point out that falconry by all evidences was imported from the East, and the Germans got it from the Romans, not the other way round.
falciform: "Curved like a sickle; hooked", Mid 18th century: from Latin falx, falc- 'sickle' + -iform.