Mythical creature, fabulous bird, displayed over in a French home (7)
I believe the answer is:
unicorn
'mythical creature' is the definition.
(I've seen this before)
'fabulous bird displayed over in a french home' is the wordplay.
'fabulous bird' becomes 'roc' (mythical or fabulous giant bird).
'displayed over' says the letters should be written backwards (letters flipped back or over).
'in' means one lot of letters goes inside another.
'a french' becomes 'un' ('a' in French).
'home' becomes 'in' ('he's home' can mean 'he's in').
'roc' reversed gives 'cor'.
'un'+'in'='unin'
'cor' going into 'unin' is 'UNICORN'.
(Other definitions for unicorn that I've seen before include "Fabulous beast like one-horned horse" , "Fabulous horned animal" , "Legendary one-horned horse" , "Mythical and heraldic beast" , "Imaginary creature with one horn" .)