1540s, "a handbook," from Late Latin, from Greek enkheiridion, neuter of enkheiridios "that which is held in the hand," from en "in" (see en- (2)) + kheir "hand" (from PIE root *ghes- "the hand") + diminutive suffix -idion.
word-forming element meaning "near, at, in, on, within," from Greek en "in," cognate with Latin in (from PIE root *en "in"), and thus with en- (1). Typically assimilated to em- before -p-, -b-, -m-, -l-, and -r-.
Old English handboc "handbook, manual;" see hand (n.) + book (n.). It translates Latin manualis, and was displaced in Middle English by manual (from French), and later in part by enchiridion (from Greek). Reintroduced 1814 in imitation of German Handbuch, but execrated through much of 19c. as "that very ugly and very unnecessary word" [Richard Chenevix Trench, "English Past and Present," 1905].
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Harper, D. (n.d.). Etymology of enchiridion. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/enchiridion