Poles in play with Greek character (7)
I believe the answer is:
epsilon
'greek character' is the definition.
(letter from the Greek alphabet)
'poles in play' is the wordplay.
'play' indicates an anagram.
'poles'+'in'='polesin'
'polesin' anagrammed gives 'EPSILON'.
'with' acts as a link.
(Other definitions for epsilon that I've seen before include "Greek letter E" , "Greek letter - pinoles (anag)" , "One's lip (anag)" , "Foreign character" , "Lose pin (anag.)" .)