Devote time to break useless caddie's resolve finally (8)
I believe the answer is:
dedicate
'devote' is the definition.
(I know that devote can be written as dedicate)
'time to break useless caddie's resolve finally' is the wordplay.
'time' becomes 't' (abbreviation).
'to break' indicates putting letters inside (inserted letters break into the word).
'useless' indicates an anagram.
'finally' suggests the final letters.
The last letter of 'resolve' is 'e'.
'caddie'+'e'='caddiee'
'caddiee' with letters rearranged gives 'dedicae'.
't' put into 'dedicae' is 'DEDICATE'.
(Other definitions for dedicate that I've seen before include "Devote to a sacred person or use" , "Devote, address, to" , "Commit" , "Inscribe or give over to" , "Devote to a special purpose, say time or energy" .)