A little nipper trapped between poles (7)
I believe the answer is:
smidgen
'a little' is the definition.
(thesaurus)
'nipper trapped between poles' is the wordplay.
'nipper' becomes 'midge' (insect which might nip you).
'trapped between' means one lot of letters goes inside another.
'poles' becomes 'SN' (North and South poles).
'midge' going within 'sn' is 'SMIDGEN'.
(Other definitions for smidgen that I've seen before include "Scarcely detectable amount" , "Iota" , "Very little" , "bit!" , "Taste" .)