You say that behaviour or a decision is fair when it is reasonable, right, or just.
Don't use 'fair' as an adverb, except in the expression play fair. If you want to say that something is done in a reasonable or just way, the word you use is fairly.
Fairly also has a completely different meaning. It means 'to quite a large degree'.
Be Careful!
Don't use 'fairly' in front of a comparative form. Don't say, for example, 'The train is fairly quicker than the bus'. In conversation and less formal writing, you say 'The train is a bit quicker than the bus'.
Be Careful!
In more formal writing, you use rather or somewhat.
Many other words and expressions can be used to show degree.
| Adv. | 1. | fairly - to a moderately sufficient extent or degree; "pretty big"; "pretty bad"; "jolly decent of him"; "the shoes are priced reasonably"; "he is fairly clever with computers" |
| 2. | fairly - without favoring one party, in a fair evenhanded manner; "deal fairly with one another" | |
| 3. | fairly - in conformity with the rules or laws and without fraud or cheating; "they played fairly" below the belt, unfairly - in an unfair manner; "they dealt with him unfairly"; "their accusations hit below the belt" |