Attack daily grind enthusiastically at first (6)
I believe the answer is:
charge
'attack' is the definition.
(I've seen this before)
'daily grind enthusiastically at first' is the wordplay.
'daily' becomes 'char' (I've seen this before).
'at first' suggests taking the first letters.
The first letters of 'grind enthusiastically' is 'ge'.
'char'+'ge'='CHARGE'
(Other definitions for charge that I've seen before include "Formally accuse; rush" , "Rush to exact payment?" , "person in custody" , "Lord Cardigan's order to his brigade" , "Fix as a price or accuse" .)