Appropriate small duck (5)
I believe the answer is:
'appropriate' is the definition.
(appropriate can mean to steal)
'small duck' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'duck' becomes 'teal' (teal is a type of duck).
(Other definitions for steal that I've seen before include "Take illegally" , "Plagiarise" , "Lift - pocket" , "a snip!" , "Pilfer" .)