Pole with spike for blind (5)
I believe the answer is:
swear
'blind' is the definition.
('blind' means 'swear' as in 'effing and blinding')
'pole with spike' is the wordplay.
'pole' becomes 's' (abbreviation for South, as in South Pole).
'with' becomes 'w' (abbreviation).
'spike' becomes 'ear' (spike is another term for an ear of grain).
's'+'w'+'ear'='SWEAR'
'for' is the link.
(Other definitions for swear that I've seen before include "Eff and blind" , "Affirm" , "Use bad language" , "Use indecent or blasphemous language" , "Vow, attest" .)