The Collaborative International Dictionary of English v.0.48:

Pectoral \Pec"to*ral\ (p[e^]k"t[-o]*ral), a. [L. pectoralis, fr.
   pectus, -oris the breast; cf. F. pectoral.]
   1. Of or pertaining to the breast, or chest; as, the pectoral
      muscles.
      [1913 Webster]

   2. Relating to, or good for, diseases of the chest or lungs;
      as, a pectoral remedy.
      [1913 Webster]

   3. (Zool.) Having the breast conspicuously colored; as, the
      pectoral sandpiper.
      [1913 Webster]

   Pectoral arch, or Pectoral girdle (Anat.), the two or
      more bony or cartilaginous pieces of the vertebrate
      skeleton to which the fore limbs are articulated; the
      shoulder girdle. In man it consists of two bones, the
      scapula and clavicle, on each side.

   Pectoral cross (Eccl.), a cross worn on the breast by
      bishops and abbots, and sometimes also by canons.

   Pectoral fins, or Pectorals (Zool.), fins situated on the
      sides, behind the gills. See Illust. under Fin.

   Pectoral rail. (Zool.) See Land rail
      (b) under Land.

   Pectoral sandpiper (Zool.), the jacksnipe
      (b) .
          [1913 Webster]

WordNet (r) 3.0 (2006):

pectoral arch
    n 1: the bony arch formed by the collarbones and shoulder blades
         in humans [syn: shoulder girdle, pectoral arch]