Saw some Canada geese (5)
I believe the answer is:
adage
'saw' is the definition.
(saw can mean a proverb or saying)
'some canada geese' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ADAGE' is hidden within 'canada geese'.
(Other definitions for adage that I've seen before include "Saying, saw" , "True proverb or saying" , "Axiom" , "Proverb, maxim" , "Saw, proverb" .)