From Middle English schakkyl, schakle, from Old English sċeacel, sċeacul, sċacul, from Proto-West Germanic *skakul, from Proto-Germanic *skakulaz ("shackle"), from Proto-Indo-European *skeg-, *skek-, equivalent to shake + -le. Cognate with Dutch schakel ("link, shackle, clasp"), German Schäckel ("shackle"), Danish skagle ("a carriage trace"), Swedish skakel ("the loose shaft of a carriage"), Icelandic skökull ("a carriage pole").
From Middle English schakelen, schakkylen, from the noun (see above).