Compassion to get small suit (6)
I believe the answer is:
hearts
'suit' is the definition.
(I've seen this before)
'compassion to get small' is the wordplay.
'compassion' becomes 'heart' (I've seen this before).
'to get' says to put letters next to each other.
'small' becomes 's' (abbreviation - e.g. clothes size).
'heart'+'s'='HEARTS'
(Other definitions for hearts that I've seen before include "Red playing cards" , "Card suit and essential organs" , "Vital organs in the pack" , "Body pumps" , "Suit for vital organs" .)