fellow member,
member an organization that is a member of another organization (especially a state that belongs to a group of nations); "the library was a member of the interlibrary loan association"; "Canada is a member of the United Nations"
committee,
commission a special group delegated to consider some matter; "a committee is a group that keeps minutes and loses hours" - Milton Berle
Commissioner is in principle the title given to a member of a commission or to an individual who has been given a commission (official charge or authority to do something, the noun's second meaning). In practice the title of commissioner has evolved to include a variety of senior officials, often sitting on a specific commission. In particular, commissioner frequently refers to senior police or government officials.
