MP given support in UN? Plenty! (7)

I believe the answer is:

umpteen

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'mp given support in un? plenty' is the definition.
I can't judge whether this definition defines the answer.

'mp given support in un?' is the wordplay.
'given' is a charade indicator (letters next to each other).
'support' becomes 'tee' (tee is a kind of support).
'in' indicates putting letters inside.
'mp'+'tee'='mptee'
'mptee' going within 'un' is 'UMPTEEN'.

Can you help me to learn more?

(Other definitions for umpteen that I've seen before include "Guarded" , "Large but indefinite number" , "Great in number but unspecified" , "Unspecified large number" , "Countless" .)

I've seen this clue in The Times.

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