He signals decline lots of people curtailed (7)

I believe the answer is:

flagman

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'he signals' is the definition.
The definition suggests a singular noun which matches the answer.

'decline lots of people curtailed' is the wordplay.
'decline' becomes 'flag'.
'lots of people' becomes 'many' (many people).
'curtailed' means to remove the last letter.
'many' with its last letter removed is 'man'.
'flag'+'man'='FLAGMAN'

Can you help me to learn more?

(Another definition for flagman that I've seen is " Signaller".)

I've seen this clue in The Independent.

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