Monsieur backing attempt to get the French shrub (6)
I believe the answer is:
myrtle
'shrub' is the definition.
(myrtle is a kind of shrub)
'monsieur backing attempt to get the french' is the wordplay.
'monsieur' becomes 'm' (French abbreviation - like Mr for Mister).
'backing' says the letters should be written in reverse.
'attempt to' becomes 'try' (I've seen this in other clues).
'get' means one lot of letters go next to another.
'the french' becomes 'le' ('the' in French).
'try' back-to-front is 'yrt'.
'm'+'yrt'+'le'='MYRTLE'
(Other definitions for myrtle that I've seen before include "Shrub; female name" , "Maybe miss" , "Try Mel for the flowering shrub" , "Shrub with white flowers and aromatic berries" , "Fragrant evergreen shrub" .)