[ mas-lis ]
/ ˈmæs lɪs /
pertaining to an elementary particle having zero rest mass, as a photon.
Related formsmass·less·ness, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for massless
In the inside of one there are fly-wheels, in the inside of the other a massless spring.