Spotter
WordNet
noun
(1) Someone who is the first to observe something
(2) A person employed to watch for something to happen
(3) A worker employed to apply spots (as markers or identifiers)
(4) A worker employed at a dry-cleaning establishment to remove spots
WiktionaryText
Noun
- a person who observes something
- a member of a sniper team
- a person who stands by the person performing an activity, in order to help them should they be unable to complete the exercise properly.