[common; from mathematical usage] Combining simplicity, power, and a certain ineffable grace of design. Higher praise than ‘clever’, ‘winning’, or even cuspy.

The French aviator, adventurer, and author Antoine de Saint-Exupéry, probably best known for his classic children's book The Little Prince, was also an aircraft designer. He gave us perhaps the best definition of engineering elegance when he said “A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away.”