Heartless relative gets a quiet release (7)
I believe the answer is:
unleash
'release' is the definition.
(I know this)
'heartless relative gets a quiet' is the wordplay.
'heartless' says to hollow out the word (remove centre letters).
'relative' becomes 'uncle' (uncle is a kind of relative).
'gets a quiet' becomes 'ash' (I can't justify this - if you can you should believe this answer much more).
'uncle' with its centre taken out is 'unle'.
'unle'+'ash'='UNLEASH'
Can you help me to learn more?
(Other definitions for unleash that I've seen before include "Free from control" , "Flee from restraint, allow to pursue like dog" , "Let free" , "Let loose" , "Let off the lead" .)