pectus

Pectus, pectoris, n., third declension neuter, so the nominative and accusative are identical in both numbers: pectus in the singular, pectora in the plural. The stem pector- carries the rest.

Anatomically it is the ribcage, the front of the chest. In the poets and in prose alike it is also where thought and feeling live, so a mind full of courage is a pectus rather than a cor, and the Latin for learning something by heart runs through it. That gives translators a choice on almost every appearance: chest, breast or heart, and the wrong one flattens the line. English pectoral and expectorate come from the same word, which is a fair reminder that the Latin starts with the bone and only then moves inwards.