Guns old earl's taken into battle for treasure (6,2,5)
I believe the answer is:
pieces of eight
'treasure' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'guns old earl's taken into battle' is the wordplay.
I cannot really understand how this works, but
'guns' could be 'pieces' (piece is a kind of gun) and 'pieces' is present in the answer.
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is found in the answer.
'earl' could be 'e' and 'e' is located in the answer.
'battle' could be 'fight' (synonyms) and 'fight' is present in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'for' is the link.
Can you help me to learn more?
(Other definitions for pieces of eight that I've seen before include "Old Spanish silver coins" , "Old Spanish coins (sought by pirates)" , "Old coins; '---!' (Long John Silver's parrot)" , "2 and 6 perhaps" , "Spanish dollars" .)