Spectator's greeting heard (7)

I believe the answer is:

watcher

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'spectator's' is the definition.
(thesaurus)

I don't understand how the remainder of the clue works.

(Other definitions for watcher that I've seen before include "I observe" , "Big Brother?" , "One who observes" , "Alert observer" , "Onlooker" .)

I've seen this clue in The Sun.

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