Pledge a letter for special body (9)

I believe the answer is:

committee

I'm a little stuck... Click here to teach me more about this clue!

'special body' is the definition.
'committee' can be an answer for 'body' (thesaurus). I am unsure of the 'special' bit.

'pledge a letter' is the wordplay.
'pledge' becomes 'commit' (I've seen this in another clue).
'a letter' becomes 'tee' (I've seen this in other clues).
'commit'+'tee'='COMMITTEE'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for committee that I've seen before include "governance team" , "working group" , "Executive group" , "Parliamentary group" , "Group delegated to consider matters" .)

I've seen this clue in the Sydney Morning Herald.

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