Boil crab pureed by relative (9)
I believe the answer is:
carbuncle
'boil' is the definition.
(I've seen this before)
'crab pureed by relative' is the wordplay.
I cannot really understand how this works, but
an anagram of 'crab' is 'carb' which is located in the answer.
'relative' could be 'uncle' (uncle is a kind of relative) and 'uncle' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for carbuncle that I've seen before include "eyesore architecturally" , "Red gemstone; sort of boil" , "cheaper jewel?" , "Sort of boil; a gem" , "Cluster of boils - jewel" .)