Best postage of junior form armour (5,5,4)
I believe the answer is:
first class mail
'best postage of junior form armour' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'best postage of junior form armour' is the wordplay.
I cannot quite understand how this works, but
'best' could be 'first' (similar in meaning) and 'first' is present in the answer.
'form' could be 'class' (synonyms) and 'class' is present in the answer.
'armour' could be 'mail' (mail is a kind of armour) and 'mail' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for first class mail that I've seen is " important post".)