[n] someone who takes the place of another person
[adj] (botany) of leaves and branches etc; first on one side and then on the other in two ranks along an axis; not paired; "stems with alternate leaves"
[adj] allowing a choice; "an alternative plan"
[v] reverse, as of direction, attitude, or course of action
[v] do something in turns; "We take turns on the night shift"
[v] go back and forth; swing back and forth between two states or conditions
[v] be an understudy or alternate for a role
[v] exchange people temporarily to fulfill certain jobs and functions
alternative, flip, flip-flop, interchange, jump, replacement, secondary, surrogate, switch, tack, take turns, understudy
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, circ