The term 'FUNDAMENTAL RULES' can be broken down into two words, 'FUNDAMENTAL' and 'RULES'. The word 'FUNDAMENTAL' is defined as something that is essential or basic, while the word 'RULES' refers to regulations or guidelines. Together, these two words refer to a set of RULES that are essential for governing a particular system or activity. The crossword solution for this term is 'CANONS', which is defined as a set of principles or RULES that are accepted as authoritative. In other words, CANONS are a set of FUNDAMENTAL RULES that are accepted as authoritative and must be followed.