The word "every" in the sentence "Every man must die" is a distributive adjective. Distributive adjectives indicate that something applies to each and every member of a group. In this case, the adjective "every" is used to indicate that the verb "must die" applies to each and every man.

The other options are incorrect. Demonstrative adjectives indicate which particular thing or person is being referred to (e.g., "this", "that", "these", "those"). Possessive adjectives indicate ownership (e.g., "my", "his", "her", "its", "our", "their"). Descriptive adjectives describe something (e.g., "tall", "short", "red", "blue"). Numeral adjectives indicate quantity (e.g., "one", "two", "three", "four").