Flipping excellent mushrooms eaten by the French in particular (8)
I believe the answer is:
especial
'particular' is the definition.
(synonyms)
'flipping excellent mushrooms eaten by the french' is the wordplay.
'flipping' is a reversal indicator.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'mushrooms' becomes 'ceps' (I've seen this before).
'eaten by' is an insertion indicator.
'the french' becomes 'le' ('the' in French).
'ai'+'ceps'='aiceps'
'aiceps' placed inside 'le' is 'laicepse'.
'laicepse' written backwards gives 'ESPECIAL'.
'in' is the link.
(Other definitions for especial that I've seen before include "Spice ale wrongly and be particular" , "Unusual" , "Over and above what is usually expected" , "Notable; for one person or thing only" , "Exclusive" .)