D defs.my
Entry 2 senses Webster, 1913

Relativistic

/rĕlˌ-ət-ĭv-ĭs'-tĭk/ · Rel·a·tiv·ist·ic · IPA /ˈɹɛl.ə.təˌvɪst.ɪk/
01 a. of, pertaining to, or in conformity with the theory of relativity; as, the relativistic increase of mass with velocity.
  1. 1.
    of, pertaining to, or in conformity with the theory of relativity; as, the relativistic increase of mass with velocity. See: theory of relativity
  2. 2.
    moving at a speed sufficiently high that the changes of mass or time dilation predicted by the theory of relativity may be observed; moving at a significant fraction of the speed of light; as, relativistic electrons.