advocate, agent, alter ego, alternating, alternative, amicus curiae, analogy, attorney, back and fill, back-and-forth, backup, backup man, bandy, battledore and shuttlecock, be here again, be quits with, beating, champion, change, changeling, circle, circling, come again, come and go, come around, come round, come round again, come up again, commute, comparison, compensate, complementary, cooperate, copy, corresponding, counterchange, counterfeit, cover, cycle, cyclic, deputy, dither, do a hitch, do a stint, do a tour, do time, double, dummy, ebb and flow, enlist, epochal, equal, equivalent, equivocate, ersatz, even, every other, exchange, exchangeable, executive officer, exponent, fake, figurehead, fill in for, fill-in, flounder, fluctuate, get back at, get even with, ghost, ghostwriter, give and take, go through phases, have a go, have tenure, hitch and hike, hold office, imitation, in rotation, interchange, interchangeable, intermit, intermittent, isochronal, isochronous, keep a watch, lieutenant, locum, locum tenens, logroll, makeshift, measured, metaphor, metonymy, metronomic, mock, next best thing, oscillate, oscillatory, other, paranymph, pass and repass, pay back, pendulate, periodic, periodical, permute, personnel, phony, pinch, pinch hitter, pleader, procurator, provisional, proxy, pulsate, pulse, pulsing, re-up, reappear, reciprocal, reciprocate, reciprocative, recur, recurrent, recurring, reenlist, relief, relieve, reoccur, repeat, replacement, replacing, representative, requite, reserve, reserves, respond, retaliate, return, return the compliment, revolve, rhythmic, ride and tie, ring the changes, ringer, roll around, rotary, rotate, rotating, seasonal, second, second in command, second string, secondary, seesaw, serial, serve time, shift, shilly-shally, shuffle, shuttle, shuttlecock, sign, sign up, sine wave, spare, spares, spell, spell off, stagger, stand-in, steady, stopgap, sub, substituent, substitute, substitution, succedaneum, succeed, successive, superseder, supplanter, surrogate, swap, sway, swing, switch, symbol, synecdoche, take turns, teeter, teeter-totter, temporary, tentative, tergiversate, third string, time off, to-and-fro, token, totter, trade, transpose, turn, understudy, undulant, undulate, undulatory, up-and-down, utility, utility man, utility player, vacillate, variant, vary, vicar, vicar general, vicarious, vice, vice-president, vice-regent, vicegerent, wavelike, waver, wax and wane, wheel, wheel around, wheeling, wibble-wabble, wigwag, wobble, zigzag