observer
UK: əbˈzɜːvə | US: əbˈzɜːrvər
n. a person who watches or notices something
n. a person who attends a meeting, event, etc., to monitor but not participate
n. a member of an official team sent to monitor a situation (e.g., UN observer)
The word traces back to Latin observare, reflecting the act of careful watching. The prefix ob- intensifies the root servare (to guard), originally implying vigilant attention. Over time, "observe" expanded from literal guarding to broader scrutiny. The suffix -er (Old English -ere) later standardized its role as "one who observes."
The scientist acted as a silent observer during the experiment.
Journalists were present as observers at the peace talks.
Birdwatchers are keen observers of nature’s details.
The UN sent a team of observers to monitor the election.
As an observer, she noted patterns others overlooked.