"Namesake"

I can never keep it straight. Does "namesake" mean the person who is named after someone else OR does it mean the person someone is named after?

Apparently the answer is "no," it means the person who is named after someone else AND it means the person someone is named after.

Merriam-Webster defines 'namesake' as follows:

one that has the same name as another; especially : one who is named after another or for whom another is named

http://m-w.com/dictionary/namesake

Which sounds to me like my grandson is my son's namesake, AND my son is my grandson's namesake. No?