We don't have any synonyms for dark energy yet.
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Definition of dark energy:
(n) :
(astronomy, astrophysics) A hypothetical form of energy thought to be spread uniformly throughout space (and time) and to have anti-gravitational properties: it represents a possible mechanism for the cosmological constant, and thus is one of the possible explanations for the current accelerating rate of expansion of the universe; and it is estimated to account for about 74% of the mass-energy of the universe.