al·ter·nate 
(ôltər-nāt′, ăl-)
(ôltər-nāt′, ăl-)v. al·ter·nat·ed, al·ter·nat·ing, al·ter·nates
v.intr.
1.
a. To occur in a successive manner: day alternating with night.
b. To act or proceed by turns: The students alternated at the computer.
2. To pass back and forth from one state, action, or place to another: alternated between happiness and depression.
3. Electricity To reverse direction at regular intervals in a circuit.
v.tr.
1. To do or execute by turns.
2. To cause to alternate: alternated light and dark squares to form a pattern.
adj. (-nĭt)
1. Happening or following in turns; succeeding each other continuously: alternate seasons of the year.
2. Designating or relating to every other one of a series: alternate lines.
3. Serving or used in place of another; substitute: an alternate plan. See Usage Note at alternative.
4. Botany
a. Arranged singly at each node, as leaves or buds on different sides of a stem.
b. Arranged regularly between other parts, as stamens between petals.
n. (-nĭt)
1. A person acting in the place of another; a substitute.
2. An alternative.
[Latin alternāre, alternāt-, from alternus, by turns, from alter, other; see al-1 in the Appendix of Indo-European roots.]
alter·nate·ly adv.