Old King Lear's first to show guts (5)
I believe the answer is:
offal
'show guts' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'old king lear's first' is the wordplay.
'old king' becomes 'offa' (King of Mercia).
'lear's first' becomes 'l' (1st letter of 'lear').
'offa'+'l'='OFFAL'
'to' is the link.
Can you help me to learn more?
(Other definitions for offal that I've seen before include "Butcher's leftovers" , "Liver, lungs etc" , "Heart, liver, kidney etc" , "Edible heart, liver and tongue, for instance" , "Animal entrails and internal organs - worthless" .)