alternate
al-ter-nate
noun
A person or thing serving as a substitute or replacement.
"He was an alternate for the jury."
adjective
Happening every second one; by turns.
"We meet on alternate Tuesdays."
verb
To occur or cause to occur in sequence or turns.
"The lights alternate between red and green."
Thesaurus
Synonyms: alternative, substitute, secondary, take turns, understudy, jump, surrogate, replacement, flip, interchange, flip-flop, tack