• (n.) An experimenter. • (n.) One who experiences.
Ex·pe'ri·en·cer noun 1. One who experiences. 2. An experimenter. [ Obsolete] Sir. K. Gigby. 
a person or thing that experiences. · (in case grammar) the semantic role of a noun phrase that indicates the perceiver of the action or state of affairs specified by the verb, as the boy in The boy was warm or in The fly annoyed the boy.