Lewis & Short

praesĭdĭārĭus, a, um, adj. [praesidium].

  1. I. Lit.
      1. 1. In gen., that serves for defence or protection (not in Cic. or Cæs.): praesidiarii milites, garrison soldiers, Liv. 29, 8; cf.: dicti praesidiarii milites ante alios collocati qui erant, aut in alio loco praepositi, Fest. S. V. SVBSIDIVM, p. 306 Müll.: classis, Ascon. ad Cic. Verr. 2, 1, 34, § 86.
      2. 2. In partic., of or belonging to the governor of a province, gubernatorial (post-class.): togam praesidiariam accepit (al. praesidariam), Spart. Sev. 1.
    1. B. Subst.: praesĭdĭārĭum, ii, n., a garrison, Not. Tir. p. 56.
  2. II. Transf.: praesidarii malleoli, kept as a reserve in case the wine should fail, Col. 4, 15, 1: palmes, i. q. resex, id. 4, 21, 3.