The term 'ASSAY SUBJECT' can be broken down into two words: 'ASSAY' and 'SUBJECT'. ASSAY is a noun that refers to the testing or analysis of a substance, usually for the purpose of determining its composition or quality. The term 'SUBJECT' is a noun that refers to a person or thing that is being studied or discussed. In this case, the crossword solution for the term 'ASSAY SUBJECT' is 'ORE', which is a noun that refers to a mineral or rock that contains valuable metals or minerals that can be mined for profit.