Lewis & Short

in-vincĭbĭlis, e, adj.

  1. I. Invincible, unconquerable (post-class.): invincibile et insuperabile malum, Tert. adv. Herm. 11.
  2. II. Irrefutable: gravia et invincibilia dicere, App. Mag. p. 297.
    Adv.: invin-cĭbĭlĭter, irrefutably, App. Flor. p. 360, 31.