virial
One-half of the product of the stress of attraction or repulsion with the distance between two particles.
The quantity 1/2 Rr, or half the product of the attraction into the distance across which the attraction is exerted, is defined by Clausis [Prof. Clausis of Bonn] as the virial of the attraction. (In the case of pressure or repulsion, the virial is negative.)
Where it comes from
From Latin vīs (vīs has a hidden "r" that shows in forms such as the genitive plural, vīrium).
Adapted from the Wiktionary entry virial (CC BY-SA 4.0).