rest energy restem • restep · · · Info · Definitions · Characters · · rest energy · · Text Common · · Latin · · Scripts 11 · · Length 4 · · Syllables Definitions · · · (noun) the energy equivalent to the mass of a particle at rest in an inertial frame of reference; equal to the rest mass times the square of the speed of light. Synonyms: rest energy. · · Noun Definition 1 Characters · · space U+0020 e latin small letter e U+0065 g latin small letter g U+0067 n latin small letter n U+006E r latin small letter r U+0072 s latin small letter s U+0073 t latin small letter t U+0074 y latin small letter y U+0079