Synonyms and related words :
alternate, alternately, back-and-forth, backward and forward, backwards and forwards, capriciously, changeably, desultorily, erratically, hitch and hike, in and out, inconstantly, mutatis mutandis, off and on, on and off, reciprocal, reciprocally, reciprocative, ride and tie, round and round, seesaw, shuttlewise, sine wave, to and fro, to-and-fro, uncertainly, unsteadfastly, unsteadily, up and down, up-and-down, variably, vice versa, waveringly