discharge (v.)youdaoicibaDictYouDict[discharge 词源字典]
early 14c., "to exempt, exonerate, release," from Old French deschargier (12c., Modern French décharger) "to unload, discharge," from Late Latin discarricare, from dis- "do the opposite of" (see dis-) + carricare "load" (see charge (v.)).

Meaning "to unload, to free from" is late 14c. Of weapons, from 1550s. The electrical sense is first attested 1748. Meaning "to fulfill, to perform one's duties" is from c. 1400. Related: Discharged; discharging.[discharge etymology, discharge origin, 英语词源]
discharge (n.)youdaoicibaDictYouDict
late 14c., "relief from misfortune," see discharge (v.). Meaning "release from work or duty" is from early 15c.