From Middle Dutch keer, kere, ultimately a derivative of Dutch keren (“to turn around, revolve”). Compare German Low German Kehr (“time, turn”), German Kehr (“turn, direction”), Old English ċierr ("turn, time, occasion"; > English chore).
The singular form is normally used after numerals. Thus: vele keren – many times; but: drie keer – three times (lit. three-time).
See the etymology of the main entry.