whimsical

determined by chance or impulse or whim rather than by necessity or reason

Full of, or characterized by, whims; actuated by a whim; having peculiar notions; queer; strange; freakish.

from Latin 'vis' meaning force or impulse

“Romfrey, with a whimsical shrewd cast of the eye at Beauchamp, who stood alert not to be foiled, arrow-like in look and readiness to repeat his home-shot.”

— George Meredith, Complete Project Gutenberg Works of George Meredith

In Abuja's bustling market, Alejandro spotted a whimsical hat shop. The hats were as impulsive as gusts of wind— one moment a top hat, the next a floppy beret. Each day, he visited, leaving with something new, much to his coworkers' confusion and delight.

Khalid sauntered through Cairo's Khan el-Khalili market, his eyes alighting on a glittering array of colorful scarves. On a whim, he plucked a shimmering turquoise one, draping it around his neck with a flourish, his decision as whimsical as the swaying palm trees in the distance.

“The term antimatter was first used by Arthur Schuster in two rather whimsical letters to Nature in 1898, in which he coined the term.”