Got sole trading rights to wheat before the beginning of December (8)
I believe the answer is:
cornered
'got sole trading rights' is the definition.
(as in cornering the market)
'wheat before the beginning of december' is the wordplay.
'wheat' becomes 'corn' (synonyms).
'before' becomes 'ere' (poetic term for 'before').
'the beginning of' indicates taking the first letters.
The initial letter of 'december' is 'd'.
'corn'+'ere'+'d'='CORNERED'
'to' is the link.
(Other definitions for cornered that I've seen before include "Caught in a difficult position" , "Monopolised the market" , "Unable to escape" , "went round the bend" , "In an awkward position" .)