grandmother
Concise Oxford English Dictionary © 2008 Oxford University Press:
grandmother/ˈɡranmʌðə(r)/
▶noun the mother of one's father or mother.
– phrases
teach one's grandmother to suck eggs presume to advise a more experienced person.
teach one's grandmother to suck eggs presume to advise a more experienced person.
– derivatives
grandmotherly adjective.
grandmotherly adjective.
'grandmother' also found in these Oxford entries:

