whim /wɪm/ BrE AmE noun [countable]
[ Date: 1600-1700 ; Origin: whim-wham 'decorative object, whim' (16-19 centuries) , of unknown origin ]
a sudden feeling that you would like to do or have something, especially when there is no important or good reason
on a whim
I didn’t leave just on a whim (=for no good reason) .
at the whim of somebody
At work they are at the whim of the boss.
sb’s every whim
Their father had always indulged her every whim.
at whim
He appeared and disappeared at whim.