Lewis & Short

per-lībro, āvi, ātum, 1, v. a., to make exactly level, to level.

  1. I. Lit., Col. 3, 13, 13: permensum et perlibratum opus, id. 3, 13 fin.: planities non perlibrata, sed exigua prona, not level, not horizontal, id. 2, 2, 1: si quis Excelsa perlibrat, Sen. Q. N. 3, 27.
  2. II. Transf., to hurl with a vibratory motion (poet.): saevamque bipennem Perlibrans mediae fronti, Sil. 2, 189: hastam, id. 5, 321: jaculum a tergo ad ossa, id. 15, 699.