Plan beginning to disappoint large number (5)

I believe the answer is:

draft

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'plan' is the definition.
(drafting is a kind of planning)

'beginning to disappoint large number' is the wordplay.
'beginning to' suggests taking the first letters.
'large number' becomes 'raft' (I can't explain this - if you can you should believe this answer much more).
The first letter of 'disappoint' is 'd'.
'd'+'raft'='DRAFT'

Can you help me to learn more?

(Other definitions for draft that I've seen before include "plan outlined" , "Sketch; money order" , "Formulate" , "Rough sketch" , "Bank payment order" .)

I've seen this clue in The Telegraph.

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