Lewis & Short

prō-praetor, ōris, m. (also prōprae-tōre or prō praetōre, indecl.),

  1. I. a magistrate in the times of the republic, who, after having administered the prœtorship one year in Rome, was sent in the following year as prœtor to a province where there was no army, a proprœtor (class.).
    Form propraetor: cum bella a propraetoribus administrantur, Cic. Div. 2, 36, 76.
    Form pro praetore, Sall. J. 103, 4: prorogatum Tubulo est, ut pro praetore in Etruriam succederet Calpurnio, Liv. 27, 22, 5.
  2. II. One who administers the prœtorship of a province in the absence of the prœtor: Aulo fratre in castris pro praetore relicto, Sall. J. 36, 4: quem pro praetore in castris relictum supra diximus, id. ib. 37, 3; Liv. 10, 25, 11; 29, 6, 9; Tac. A. 2, 66 al.; Caes. B. G. 1, 21.