Compatible with mass of butter (3)
I believe the answer is:
pat
'mass of butter' is the definition.
'pat' can be an answer for 'butter' (a pat can mean a lump of butter). I am unsure of the 'mass of' bit.
'compatible with' is the wordplay.
'with' indicates a hidden word.
'PAT' can be found hidden inside 'compatible'.
Can you help me to learn more?
(Other definitions for pat that I've seen before include "Knob (of butter)" , "well-rehearsed" , "Girl" , "Slick; dab" , "Gentle stroke of the hand with fluent repetition" .)