Strong and determined saint getting fish before end of day (6)
I believe the answer is:
steely
'strong' is the definition.
(I've seen this before)
'saint getting fish before end of day' is the wordplay.
'saint' becomes 'st' (abbreviation).
'getting fish before' becomes 'eel' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'end of' indicates one should take the final letters.
The final letter of 'day' is 'y'.
'st'+'eel'+'y'='STEELY'
'and determined' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for steely that I've seen before include "Set off" , "Coldly determined" , "With (cold) resolve" , "Inflexibly severe" , "As hard, or grey, as metal" .)