"spotter" in the noun sense
a worker employed at a dry-cleaning establishment to remove spots
a worker employed to apply spots (as markers or identifiers)
3. lookout, lookout man, sentinel, sentry, watch, spotter, scout, picket
a person employed to keep watch for some anticipated event
4. finder, discoverer, spotter
someone who is the first to observe something
Source: WordNet® (An amazing lexical database of English)
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