Bottom of a shoe (4)
I believe the answer is:
'bottom of a shoe' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sole that I've seen before include "Unique" , "Exclusive class of fish" , "European flatfish" , "fish > that's never less than foot in length" , "One and only; part of foot" .)