Lewis & Short

ŏnĕrōsus, a, um, adj. [onus], burdensome, heavy, oppressive (poet. and in postAug. prose; syn.: gravis, difficilis).

  1. I. Lit.: praeda, Verg. A. 9, 384.
    Of food that is difficult of digestion and causes oppression: cibus etiam valentibus onerosus, Plin. 23, 7, 62, § 115: (ervum) capiti et stomacho onerosum, id. 22, 25, 73, § 153.
    Comp.: aër est onerosior igni, Ov. M. 1, 53.
  2. II. Trop., burdensome, onerous, irksome: onerosior altera sors est, Ov. M. 9, 675: donatio, Plin. Ep. 2, 4, 3: quam sit onerosum succedere bono principi, id. Pan. 44, 7: consolatores, Vulg. Job, 16, 2.
    Hence, adv.: ŏnĕrōsē, odiously (post-class.), Paul. Nol. Ep. 11.
    Comp.: onerosius, Cassiod. Anim. 11.