Synonyms/Hypernyms (Ordered by Estimated Frequency) of noun observer

2 senses of observer

Sense 1
perceiver, percipient, observer, beholder -- (a person who becomes aware (of things or events) through the senses)
       => person, individual, someone, somebody, mortal, soul -- (a human being; "there was too much for one person to do")

Sense 2
observer, commentator -- (an expert who observes and comments on something)
       => expert -- (a person with special knowledge or ability who performs skillfully)