spotter vs perceiver

spotter and perceiver both are nouns.

Word	Noun	Adjective	Verb	Adverb
spotter	Yes	No	No	No
perceiver	Yes	No	No	No

As nouns, perceiver is a hypernym of spotter; that is, perceiver is a word with a broader meaning than spotter:

spotter: someone who is the first to observe something
perceiver: a person who becomes aware (of things or events) through the senses

Other hypernyms of spotter include beholder, observer, percipient.

spotter (noun)	perceiver (noun)
someone who is the first to observe something	a person who becomes aware (of things or events) through the senses
a worker employed to apply spots (as markers or identifiers)
a worker employed at a dry-cleaning establishment to remove spots
a person employed to keep watch for some anticipated event