Firm desirous feeling oddly to the veg (9)
I believe the answer is:
courgette
'veg' is the definition.
(courgette is a kind of vegetable)
'firm desirous feeling oddly to the' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'desirous feeling' becomes 'urge' (I can't justify this - if you can you should give a lot more credence to this answer).
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
'to'+'the'='tothe'
The alternate letters of 'tothe' are 'tte'.
'co'+'urge'+'tte'='COURGETTE'
Can you help me to learn more?
(Other definitions for courgette that I've seen before include "Type of vegetable marrow" , "Zuccini" , "this could supply kitchen" , "Small marrow" , "Zucchini is its American equivalent" .)