Hold up small bouquet (10)
I believe the answer is:
'bouquet' is the definition.
'hold up small' is the wordplay.
I cannot quite understand how this works, but
'hold' could be 'butt' (butt is a kind of hold) and 'butt' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for buttonhole that I've seen before include "Small slit in a coat lapel - detain in conversation" , "Accost" , "as Ancient Mariner did wedding guests?" , "Detain someone in conversation" , "carnation, typically" .)