They contain many a number here! (8)
I believe the answer is:
brackets
'they' is the definition.
Both the definition and answer are plural nouns.
Maybe you can see an association between them that I can't see?
'contain many a number here' is the wordplay.
I cannot really understand how this works, but
'many' could be 'c' (C is the Roman numeral for 100) and 'c' is found within the answer.
'a' is within the answer.
'number' could be 'k' (K is an example) and 'k' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for brackets that I've seen before include "Projecting supports, for a shelf say" , "eight here in these" .)