grandad
Concise Oxford English Dictionary © 2008 Oxford University Press:
grandad /ˈɡrandad/ (also granddad)
▶noun
- 1 informal one's grandfather.
- 2 [as modifier] denoting a style of shirt or neckline with a collar in the form of a narrow upright band fastened with a button.
'grandad' also found in these Oxford entries:

