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

A pattern of alternate black and white stripes has a black stripe, then a white stripe, another black stripe, another white stripe, and so on. 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.

1. Frost splits rock, so does alternate intense heat and cold.
2. He played alternate balls left- and right-handed.
3. These courses are available in alternate years.

You use alternative to describe something that can be used, had, or done instead of something else. For example, an alternative plan is a plan that could be used instead of another one. If you look for an alternative route, you know about one route but you want another one, perhaps because the first one is closed.

1. Propose alternative solutions and test them.
2. There was no alternative site for a third London airport

Alternative can also be used as a noun, meaning something else that can be chosen instead.

3. The other alternative was to wait until July.
4. There was absolutely no alternative but to go ahead.

You can also say that someone has two or more alternatives, meaning that they have two or more courses of action to choose from. This use is now quite common, although in the past it was considered incorrect.

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

You can also talk about an alternative lifestyle or an alternative society, meaning one which is different from the traditional one and which some people think is better.

6. …the supporters of Alternative Schooling.

* Some English speakers use alternate to describe something that can be used, had, or done instead of something else. This is not very common; you normally use alternative.

7. …the development of alternate energy sources.

Alternate can also be used as a verb. When you alternate between two things, you regularly do or use one thing and then the other.

8. They alternated between patronising us and ignoring us.
9. The post of president should alternate between a Greek and a Turk.

When one thing alternates with another, the two things regularly occur in turn.

10. The Third World staffers from an annual cycle of drought alternating with flood.

Other words

Instead of saying that you do something on alternate days or during alternate weeks or years, you can say you do it ‘every other’ day, week, or year.

11. We only save enough money to take a real vacation every other year.