One addict, I fancy, could show this (10)
I believe the answer is:
Here is my best explanation:
'could show this' is the definition.
The definition suggests a singular noun which matches the answer.
'one addict i fancy' is the subsidiary indication.
'fancy' indicates anagramming the letters.
'oneaddicti' anagrammed gives 'dedication'.
(Other definitions for dedication that I've seen before include "Commitment; inscription", "with which author often starts work", "tribute", "commitment" and "Devotion (to a task)".)