Lewis & Short

dissĭmŭlātĭo, ōnis, f. [dissimulo],

  1. I. a dissembling, concealing, disguising, dissimulation (good prose).
    1. A. In gen., Cic. Off. 3, 15; id. de Or. 2, 67; Quint. 6, 3, 85; Tac. A. 11, 26: veste servili in dissimulationem sui compositus, id. ib. 13, 25; id. H. 4, 18; id. A. 6, 18 fin.
    2. B. In partic., the Socratic εἰρωνεία, Cic. Ac. 2, 5, 15; Quint. 9, 1, 29; but too restricted for that idea, acc. to Quint. 9, 2, 44.
  2. II. A disregarding, Plin. Ep. 9, 13, 21.
    1. B. In late Lat., negligence, carelessness, Veg. Vet. 6 prooem. § 1; so ib. § 3; id. Mil. 1, 18.