Extremely lazy attempt by the French to conserve unity (4,4)
I believe the answer is:
bone idle
'extremely lazy' is the definition.
(bone idle means very lazy)
'attempt by the french to conserve unity' is the wordplay.
'attempt' becomes 'bid' (bid is a kind of attempt).
'by' means one lot of letters go next to another.
'the french' becomes 'le' ('the' in French).
'to conserve' means one lot of letters goes inside another.
'unity' becomes 'one' (synonyms).
'bid'+'le'='bidle'
'bidle' going around 'one' is 'BONE-IDLE'.
(Other definitions for bone idle that I've seen before include "Altogether lazy, in an ossified way" , "Very lazy from the inside out" , "Extremely lazy" , "Utterly lazy, won't do a tap" , "staff may be?" .)