Hardy character keeping fit ultimately for trials (5)
I believe the answer is:
tests
'for trials' is the definition.
('test' can be a synonym of 'trial')
'hardy character keeping fit ultimately' is the wordplay.
'hardy character' becomes 'tess' (in Tess of the d'Urbervilles, Thomas Hardy novel).
'keeping' means one lot of letters goes inside another (some letters kept inside).
'ultimately' indicates one should take the final letters.
The final letter of 'fit' is 't'.
'tess' placed around 't' is 'TESTS'.
(Other definitions for tests that I've seen before include "Tries out" , "Puts to proof at cricket matches" , "Trials to see if something works" , "International cricket matches" , "Trials -- tribulations" .)