guard ‧ i ‧ an /ˈɡɑːdiən $ ˈɡɑːr-/ BrE AmE noun [countable]
1 . someone who is legally responsible for looking after someone else’s child, especially after the child’s parents have died
sb’s guardian
His aunt is his legal guardian.
2 . formal someone who guards or protects something
guardian of
The US sees itself as the guardian of democracy.