A whim is a strange or capricious notion; a temporary eccentricity; a freak. A person or thing that has many whims can be called whimsical.
When the Web site that he started on a whim, HOTorNOT.com, a meeting site popular with 20-year-olds, unexpectedly made James Hong a millionaire, he wanted to donate some of his newfound wealth toward good causes. (NY Times)
A South Carolina woman’s whimsical approach to food is helping her crack the insular world of cooking contests with such novel dishes as pecan-encrusted oysters over asiago cheese grits. (USA Today)