Far from slender odds? Definitely not! (3,6)
I believe the answer is:
fat chance
'definitely not' is the definition.
(informal phrase to suggest something won't happen)
'far from slender odds?' is the wordplay.
'far from slender' becomes 'fat'.
'odds?' becomes 'chance' (I've seen this before).
'fat'+'chance'='FAT CHANCE'
(Other definitions for fat chance that I've seen before include "No likelihood at all!" , "Little prospect" , "that won't happen" , "Slim hope, paradoxically!" , "It will never happen!" .)