Poles are small traps (6)
I believe the answer is:
snares
'traps' is the definition.
(I know this)
'poles are small' is the wordplay.
'poles' becomes 'SN' (North and South poles).
'small' becomes 's' (abbreviation - e.g. clothes size).
'sn'+'are'+'s'='SNARES'
(Other definitions for snares that I've seen before include "Traps set by Nasser" , "Game traps" , "Lures or entanglements" , "Animal traps" , "hidden dangers" .)