Lewis & Short

pectŏrālis, e, adj. [pectus],

  1. I. of or belonging to the breast, breast-, pectoral: pectorale os, the breast-bone, Cels. 8, 1: tunicula, Amm. 14, 9, 7: cinctum, App. M. 11, p. 261, 36: fascia, Vulg. Isa. 3, 24 (Hier. in loc., Vulg. Jer. 2, 32).
    Hence,
  2. II. Subst.: pectŏrāle, is, n., a breast-plate, Varr. L. L. 5, § 115 Müll.; Plin. 34, 7, 18, § 43.