Whim; noun

a sudden idea to do something

I'd planned to clean out my closet today, but on a whim, I decided to go roller-skating.

Expressing doubt or question; puzzled

Mom looked quizzical when she received a birthday card from someone whose name she didn't recognize.

not important

When we divided the lunch bill, it seemed petty to argue over who would pay the extra five cents.

A risky or uncertain undertaking

The business venture turned out to be a finacial disaster.