lībrātor (noun M) : id..
* A leveller, esp. by means of a water-level, a surveyor, Cato, R. R. 22, 1; Front. Aquaed. 105: superest ut tu libratorem vel architectum mittas, qui diligenter exploret, sitne lacus altior mari,Plin. Ep. 10, 50, 3.
* One who throws or hurls weapons by hand (cf. funditor, a slinger): funditores libratoresque excutere tela et proturbare hostem jubet,Tac. A. 2, 20: libratoribus funditoribusque attributus locus,id. ib. 13, 39; Inscr. ap. Kellerm. Vigil. p. 55, n. 127.

s. TLL