alternately, au pair, by stages, by turns, consecutively, even, every other, exchangeably, hand running, hierarchically, in Indian file, in a chain, in a line, in a row, in a series, in column, in exchange, in file, in order, in return, in rotation, in sequence, in series, in single file, in succession, in turns, make and break, mutually, off and on, progressively, reciprocally, round and round, running, sequentially, serially, seriatim, step by step, successively, to and fro, turn about, up and down