Dwelt on shattering disappointment (3-4)
I believe the answer is:
let down
'disappointment' is the definition.
(I've seen this before)
'dwelt on shattering' is the wordplay.
'shattering' is an anagram indicator.
'dwelt'+'on'='dwelton'
'dwelton' with letters rearranged gives 'LET-DOWN'.
(Other definitions for let down that I've seen before include "Disappoint, betray" , "Disappoint, fail to keep promise" , "Fail to meet expectations of others" , "Disappoint or fail - or lengthen garment" , "Leave in the lurch" .)