Resolute hawk going after seconds (5)
I believe the answer is:
stout
'resolute' is the definition.
(similar in meaning)
'hawk going after seconds' is the wordplay.
'hawk' becomes 'tout' (both can mean to sell something).
'going after' is a charade indicator (letters next to each other).
'seconds' becomes 's' (abbreviation).
'tout' after 's' is 'STOUT'.
(Other definitions for stout that I've seen before include "Inured to fatigue and hardship" , "Rather fat; determined" , "drinks?" , "Dark ale" , "Overweight; porter" .)