An Etymological Dictionary of Astronomy and Astrophysics
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A hypothesized rapidly spinning doughnut-shaped mass of vaporized and molten rock formed from the collision of two planet-sized objects. In numerical simulations studying giant impacts of rotating objects, a synestia can form if the total → angular momentum is greater than the → co-rotational limit. Beyond the co-rotational limit, the velocity at the equator of a body would exceed the orbital velocity (Simon J. Lock nd Sarah T. Stewart, 2017, arXiv:1705.07858v1).

From → syn- "connected; together" + Hestia the goddess of architecture.