A large number attending party somewhere in 1A (4)

'somewhere in 1a' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'a large number attending party' is the wordplay.
I cannot quite see how this works, but
'a' is within the answer.
'number' could be 'm' (M is an example) and 'm' is present in the answer.
'party' could be 'do' (do is a kind of party) and 'do' is located in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?