The term COMMON TEST SUBJECT can be broken down into three words: COMMON, TEST, and SUBJECT. The first word, COMMON, is defined as something that is shared by two or more people or groups. The second word, TEST, is defined as an examination of a person's knowledge, skills, or abilities. The third word, SUBJECT, is defined as a branch of knowledge studied in school or college. When combined, the term COMMON TEST SUBJECT refers to a type of examination that is shared by two or more people or groups and tests their knowledge, skills, or abilities in a particular SUBJECT. The crossword solution for this term is RAT, which stands for 'regular assessment TEST'. This type of TEST is typically administered on a regular basis to measure a student's progress in a particular SUBJECT.