grand·fa·ther 
(grăndfä′thər, grăn-)
(grăndfä′thər, grăn-)n.
1. The father of one's mother or father.
2. A forefather; an ancestor.
tr.v. grand·fa·thered, grand·fa·ther·ing, grand·fa·thers
To exempt (someone or something) from a new regulation that prohibits or restricts something: The new ordinance restricts the size of billboards, but it grandfathers those erected before 1997.
[V., from GRANDFATHER CLAUSE.]