masslessadj.
/ˈmasləs/, U.S. /ˈmæsləs/ Chiefly Physics.
Having no mass.
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massless1879
1879 W. Thomson & P. G. Tait Treat. Nat. Philos. (new ed.) I: Pt. i. §345 A material particle supported by massless springs.
1933 Discovery Mar. 69/1 The negative electron, the massless unit charge of electricity, was isolated first in the Cavendish Laboratory by Sir J. J. Thomson in 1897.
1947 Mind 56 50 Consider a weight of mass m hanging downwards under gravity on a (massless) elastic strand.
1993 Discover Feb. 12/2 Neutrinos are massless, or nearly so, and they are hard to detect because they rarely interact with ordinary matter.
This entry has been updated (OED Third Edition, December 2000; most recently modified version published online March 2022).
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adj.1879