It won't be denied its association with the cavalry (5)
I believe the answer is:
twill
'it won't be denied its association' is the definition.
The definition suggests a singular noun which matches the answer.
'with the cavalry' is the wordplay.
'with' says to put letters next to each other.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'cavalry' becomes 'will' (I can't explain this - if you can you should believe this answer much more).
't' put next to 'will' is 'TWILL'.
Can you help me to learn more?
(Other definitions for twill that I've seen before include "Cloth with diagonal ribs" , "Fabric weave with parallel diagonal lines" , "Strong ridged fabric" , "Diagonal-weave fabric" , "Fabric with distinctive weave" .)