unset

unset – Delete variables 

This command removes one or more variables. Each name is a variable name, specified in any of the ways acceptable to the set command. If a name refers to an element of an array then that element is removed without affecting the rest of the array. If a name consists of an array name with no parenthesized index, then the entire array is deleted. The unset command returns an empty string as result. An error occurs if any of the variables doesn’t exist, and any variables after the non-existent one are not deleted.