Adult male turned up on peg -- Long John Silver? (7)
I believe the answer is:
amputee
'long john silver?' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'adult male turned up on peg' is the wordplay.
'adult' becomes 'a' (abbreviation).
'male' becomes 'm' (common abbreviation).
'turned' shows that the letters should be reversed in order.
'up on' becomes 'up' (similar in meaning).
'peg' becomes 'tee' (tee is a kind of peg).
'up' in reverse letter order is 'pu'.
'a'+'m'+'pu'+'tee'='AMPUTEE'
Can you help me to learn more?
(Other definitions for amputee that I've seen before include "One who's had a limb removed in surgery" , "One with missing limb" , "One who has lost a limb" , "Possible Paralympian" , "Person with limb(s) removed" .)