The term 'PRINCIPAL FORCE' can be broken down into two words, 'PRINCIPAL' and 'FORCE'. The word 'PRINCIPAL' is defined as the most important or main person in a group or organization. The word 'FORCE' is defined as an influence that causes change or produces a result. Together, the term 'PRINCIPAL FORCE' can be interpreted as the main influence that causes change or produces a result. In the crossword, the solution for this term is 'BRUNT', which means the main impact or shock of something. Therefore, the term 'PRINCIPAL FORCE' can be summarized as the main impact or shock that causes change or produces a result.