Prepared to defend cross, letting in a mere shot (9)
I believe the answer is:
forearmed
'prepared' is the definition.
(thesaurus)
'defend cross letting in a mere shot' is the wordplay.
I cannot quite understand how this works, but
'a' is within the answer.
an anagram of 'mere' is 'erme' which is present in the remaining letters.
'cross' could be 'ford' (to ford a stream is to cross it) and 'ford' is found in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'to' is the link.
Can you help me to learn more?
(Other definitions for forearmed that I've seen before include "Pre-prepared for danger" , "Prepared in advance and" , "Be forewarned and you'll be this" .)