IPA: /ˈriːdə/
KK: /ˈriːdər/
A person who reads, especially someone who enjoys reading books or other written material.
She is an avid reader who finishes several books each month.
Reader → It is formed from "read" (from Old English *rǣdan*, meaning to interpret or to advise) and "-er" (meaning a person who). A reader is a person who interprets written text.
Think of someone who 'interprets' ('read') written words — that's what a reader does.