If something is supplest, it is the most able to bend and move easily without breaking.
Being supplest is a good thing because it means something is flexible and strong at the same time.
Examples:
The cat is the supplest animal.
The supplest branches are the hardest to break.
She is the supplest dancer in the class.
The supplest rubber bands are the best for making a slingshot.
The supplest superheroes can bend steel with their hands.
The supplest gymnasts can do amazing tricks.