Ankle is treated with old patent remedy (5,3)
I believe the answer is:
snake oil
'patent remedy' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'ankle is treated with old' is the wordplay.
'treated with' is an anagram indicator.
'old' becomes 'o' (abbreviation).
'ankle'+'is'='ankleis'
'ankleis' mixed up with 'o' can make 'SNAKE-OIL'.
Can you help me to learn more?
(Other definitions for snake oil that I've seen before include "this won't make things better" , "Liquid sold as medicine but medically worthless" , "Miracle cure" .)