alternate

v.intr.

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.

n. (-nĭt)

1. A person acting in the place of another; a substitute.

2. An alternative.

vb

1. (often foll by with) to occur or cause to occur successively or by turns: day and night alternate.

2. (often foll by: between) to swing repeatedly from one condition, action, etc, to another: he alternates between success and failure.

3. (tr) to interchange regularly or in succession

4. (Electrical Engineering) (intr) (of an electric current, voltage, etc) to reverse direction or sign at regular intervals, usually sinusoidally, the instantaneous value varying continuously

5. (Theatre) theatre (often foll by: for) to understudy another actor or actress

adj

6. occurring by turns: alternate feelings of love and hate.

7. every other or second one of a series: he came to work on alternate days.

8. being a second or further choice; alternative: alternate director.

n

US and Canadian a person who substitutes for another in his absence; stand-in

11. Bot.

a. placed singly at different heights on the axis, on each side in succession, or at definite angular distances from one another, as leaves on a stem.

b. opposite to the intervals between other parts: petals alternate with sepals.

1. 'alternate'

Alternate actions, events, or processes keep happening regularly after each other.

...the alternate contraction and relaxation of muscles.

If something happens on alternate days, it happens on one day, then does not happen on the next day, then happens again on the day after it, and so on. Things can also happen in alternate weeks, months, or years.

We saw each other on alternate Sunday nights.

The two courses are available in alternate years.

2. 'alternative'

You use alternative to describe something that can be used, had, or done instead of something else.

But still people try to find alternative explanations.

There is, however, an alternative approach.

Note that in American English, alternate is sometimes used with this meaning.

How would a clever researcher rule out this alternate explanation?

Alternative can also be a noun. An alternative to something is something else that you can have or do instead.

Food suppliers are working hard to provide organic alternatives to everyday foodstuffs.

A magistrate offered them a Domestic Education course as an alternative to prison.

There is no alternative to permanent storage.

You can also say that someone has two or more alternatives, meaning that they have two or more courses of action to choose from.

If a man is threatened with attack, he has five alternatives: he can fight, flee, hide, summon help, or try to appease his attacker.

Note that it used to be considered incorrect to talk about more than two alternatives.