Also, in fun. As a joke, not seriously. For example, For fun the children told the teacher it was a holiday, or Their teasing was just in fun. [Mid-1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use for fun in a sentence
It had come from Danny, but Nan never let him know that she had received it, so his hoped-for fun over it was spoilt.The Bobbsey Twins | Laura Lee Hope
We were all in our gayest moods, and the principal page was made to sparkle with most unlooked-for fun and flashes of wit.War's Brighter Side | Julian Ralph.