Backing for Leonard enthralled by fifty karat ring (5)
I believe the answer is:
knell
'ring' is the definition.
(synonyms)
'backing for leonard enthralled by fifty karat' is the wordplay.
'backing for' shows that the letters should be reversed in order.
'leonard' becomes 'len' (I've seen this in other clues).
'enthralled by' is an insertion indicator ('enthral' can mean 'capture').
'fifty' becomes 'l' (Roman numeral).
'karat' becomes 'k' (this might be a standard abbreviation I've not previously seen).
'l'+'k'='lk'
'len' going within 'lk' is 'llenk'.
'llenk' written backwards gives 'KNELL'.
Can you help me to learn more?
(Other definitions for knell that I've seen before include "Solemn sound of a bell" , "Awesome ring" , "Toll, ring" , "Temperate" , "(Of bell) ring solemnly" .)