USAGE NOTE
The use of fun as an adjective meaning enjoyable, as in : we had a fun evening, is not fully accepted in standard English and should only be used in informal contexts. There are signs, however, that this situation is changing, given the recent appearance in American English of comparative and superlative forms funner and funnest, formed as if fun were a normal adjective. The adjectival forms funner and funnest have not 'arrived' in all the dictionaries, however, and if employed at all, they should be used sparingly and not in formal written English.