Season fresh tuna without hesitation (6)
I believe the answer is:
autumn
'season' is the definition.
(autumn is a kind of season)
'fresh tuna without hesitation' is the wordplay.
'fresh' indicates anagramming the letters.
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'hesitation' becomes 'um'.
'tuna' anagrammed gives 'autn'.
'autn' placed around 'um' is 'AUTUMN'.
(Other definitions for autumn that I've seen before include "Time of harvest" , "Season of falling leaves" , "Season, has its music too (Keats)" , "Fall for 33 across" , "Fall in the US" .)