pledge: [14] Pledge comes via Old French plege from late Latin plebium, a derivative of the verb plebīre ‘pledge’. This was probably borrowed from Frankish *plegan ‘guarantee’, a derivative of the same Germanic base as produced English plight ‘pledge’ [OE] (as in ‘plight one’s troth’) and German pflicht ‘duty’. => plight[pledge etymology, pledge origin, 英语词源]