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