A carnation primarily is fetching for buttonholes (7)
I believe the answer is:
accosts
'for buttonholes' is the definition.
(I've seen this in another clue)
'a carnation primarily is fetching' is the wordplay.
'primarily' suggests taking the first letters.
'is fetching' becomes 'costs' (I can't justify this - if you can you should believe this answer much more).
The first letter of 'carnation' is 'c'.
'a'+'c'+'costs'='ACCOSTS'
Can you help me to learn more?
(Other definitions for accosts that I've seen before include "As a solicitor does" , "Grabs" , "Approaches boldly, solicits" .)