Nanny perhaps understood about area (4)
I believe the answer is:
goat
'nanny perhaps' is the definition.
(nanny is a kind of goat)
'understood about area' is the wordplay.
'understood' becomes 'got' (getting is a kind of understanding).
'about' indicates putting letters inside.
'area' becomes 'a' (maths abbreviation).
'got' going around 'a' is 'GOAT'.
(Other definitions for goat that I've seen before include "fool" , "beast with sharp horns" , "heavenly sign" , "Domesticated animal supplying milk, meat and wool" , "foolish person" .)