Lewis & Short

confirmātor, ōris, m. [confirmo], he who confirms or establishes a thing; hence,

  1. I. Pecuniae, a surety, security, Cic. Clu. 26, 72: venditionis, Jul. Epit. Nov. c. 3, § 10.
  2. II. Trop.: sententiae, Lact. 1, 2 init.: erroris, Tert. adv. Marc. 4, 36.