The definition , the precise meaning of a term, is the means by which your reader gains understnding of your message. Clear and precise definitions are vital because they assist the reader to share the same view of the term being defined that you do. A formal definition is one sentence that contains the term being defined, the class , to which the term belongs, and the differentiation of that item from all other members of its class.
Resistance is any force that tends to oppose or retard motion.
Death is a state of existence typified by the cessation of brain and respiratory functions. Therefore, you must first Classify the Term . The class is the large group to which the term belongs. You can use either broad or narrow classes, but the narrower the class, the more meaning that will be conveyed. Then, Differentiate the Term by explaining the characteristics that belong only to it and not to any other members of the class.