complainyoudaoicibaDictYouDict[complain 词源字典]
complain: [14] Complain goes back to the Latin in verb plangere, source also of English plangent. This was formed on a prehistoric base *plak- (from which we also get plankton), and it originally meant ‘hit’. Its meaning developed metaphorically through ‘beat one’s breast’ to ‘lament’, and in medieval Latin it was combined with the intensive prefix com- to produce complangere. When it entered English via Old French complaindre it still meant ‘lament’, and although this sense had died out by about 1700, traces of it remain in ‘complain of’ a particular illness. Complaint [14] came from Old French complainte.
=> plangent, plankton[complain etymology, complain origin, 英语词源]
complain (v.)youdaoicibaDictYouDict
late 14c., "find fault, lament," from stem of Old French complaindre "to lament" (12c.), from Vulgar Latin *complangere, originally "to beat the breast," from Latin com-, intensive prefix (see com-), + plangere "to strike, beat the breast" (see plague (n.)). Older sense of "lament" died out 17c. Related: Complained; complaining.