"practicing beggary, living by alms or doles" (in reference to orders of friars), late 15c., mendicaunt, from Latin mendicantem (nominative mendicans) present participle of mendicare "to beg, ask alms," from mendicus "beggar," originally "cripple" (connection via cripples who must beg), from menda "fault, physical defect," from PIE root *mend- "physical defect, fault" (see amend (v.)).
Meaning "reduced to beggary, begging" is from 1610s. The older word in Middle English in relation to religious orders was mendinant (mid-14c.), from Old French mendinant, present participle of mendiner "to beg," from the same Latin source. The mendicant orders (freurs mendicantes or begging friars, principally the Franciscans, the Carmelites, and the Augustinians) were those religious orders which originally depended for support on the alms they received.
From 1640s as "mixed speech, pigin;" 1650s as "phraseology peculiar to a sect or profession," hence "mode of speech full of unfamiliar terms." Middle English also had it as a verb, jargounen "to chatter" (late 14c.), from French.
1706, "weakening of the eyesight without any apparent defect in the eyes," medical Latin, from Greek amblyopia "dim-sightedness," noun of action from amblys "dulled, blunt" (from a suffixed form of PIE root *mel- (1) "soft") + ōps "eye" (from PIE root *okw- "to see") + abstract noun ending -ia. Related: Amblyopic.