Strenuous effort against odds (8)
I believe the answer is:
struggle
'strenuous effort against odds' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for struggle that I've seen before include "Strive; difficult task" , "Uphill battle" , "Make strenuous efforts to overcome" , "Contend; very hard task" , "Strive - proceed with difficulty" .)