grandfather clause
noun[C]
LAWUSukus(alsograndfather provision);(alsograndfather rights[plural])apartof a newlaworrulethatallowssomeone tocontinueto do or to have something that a newlaworrulemakesillegal:
Thegrandfatherclauseappliesonly untiloffendersvoluntarilymoveorselltheirhomes.
Theolderbuildingsareexemptfrom thoserulesunder agrandfatherclause.