Adjective

1. Of or pertaining to the breast, or chest; as, the pectoral muscles.
   • 1985, Stephen Marley, Managra, p 14:

     Clad in red robes and a gold pectoral cross, Agostini finally lowered his gaze as he crossed the marble floor.

2. Relating to, or good for, diseases of the chest or lungs; as, a pectoral remedy.
3. Having the breast conspicuously colored; as, the pectoral sandpiper.

Noun

1. Protective armor for a horse's breast.
   • 1786, Francis Grose, A Treatise on Ancient Armour and Weapons, page 30:

     The Poitrinal, Pectoral, or Breast Plate was formed of plates of metal rivetted together, which covered the breast and shoulders of the horse, it was commonly adorned with foliage, or other ornaments engraved or embossed.

2. A covering or protecting for the breast.
3. A breastplate, esp. that worn by the Jewish high person.
4. A clasp or a cross worn on the breast.
5. A medicine for diseases of the chest organs, especially the lungs.