Illustrative Context

His wore a medal on his chest.

Target Sense

• The part of the human body between the shoulders and the diaphragm/upper belly (as seen from the front side, but also referring to within the rib-cage, not just in front of it — see below).
• Effectively this corresponds to the thorax in medical terminology, but following IE-CoR policy, certainly do not select such technical medical terms. Follow the basic, default register instead, i.e. English chest, definitely not thorax.
• Provide the general term for this part of the body, that can be applied to both males and females, both children and adults. Certainly do not select a lexeme that refers only, or predominantly, to the female breasts. The English lexeme for this target sense is therefore chest (not breast — see also below), in French poitrine (not sein), and in Spanish pecho (not seno). Only if a language has no common term, select the word for male chest.
• Also avoid figurative uses, senses such as English bosom, and euphemistic ones.
• The term selected should be general also in being able to refer to the part of the body within the rib cage, not just in front of it. Again, breast is thus not the right lexeme in English, since it refers primarily to the part of the body in front of the rib cage, whereas the correct chest can indeed refer to inside the rib cage too, as in a chest infection. Likewise in French, the correct word poitrine is used in, for example, angine de poitrine.
• The need for a general term also means that lexemes that apply only to inside the ribs, such as rib cage or lungs, are also to be avoided.
• Do not be confused by the potential ambiguities in English, which has both a common chest word, as well as another term breast. They are only part-synonmous, in that breast can be applied to males or females, but is also ambiguous, because in context it can also have the specific sense of the female breast, and indeed can be used in the plural. Modern usage is tending towards chest as the more general term. In this general sense, breast is becoming dated for many speakers. It remains in some fixed collocations (e.g. breast stroke in swimming), but otherwise is increasingly reserved as specific to females. (It would sound odd to say he was punched in the breast, for example. And while both sexes can suffer chest pain, the expression breast pain would normally be taken as referring to a woman only.)