Paddy takes a medium (7)
I believe the answer is:
tempera
'medium' is the definition.
(I've seen this before)
'paddy takes a' is the wordplay.
'paddy' becomes 'temper' (I've seen this in other clues).
'takes' says to put letters next to each other.
'temper'+'a'='TEMPERA'
(Other definitions for tempera that I've seen before include "Painting method using emulsion" , "Emulsion used by Renaissance painters" , "vehicle" , "Type of paint" , "A paint and a painting technique" .)