Boy quivered, intermittently showing filthy greed (8)
I believe the answer is:
cupidity
'greed' is the definition.
(cupidity is a kind of greed)
'boy quivered intermittently showing filthy' is the wordplay.
'boy quivered' becomes 'cupid' (mythical boy with a quiver of arrows).
'intermittently showing' means one should take alternating letters (letters selected on an intermittent basis).
The alternate letters of 'filthy' are 'ity'.
'cupid'+'ity'='CUPIDITY'
(Other definitions for cupidity that I've seen before include "Covetousness" , "Avarice" , "Acquisitiveness" , "Greed for money or goods" , "Desire" .)