in·sid·er \(ˈ)inˈsīdə(r), ən-\noun (-s) Etymology:inside (I) + -er : a person recognized or accepted as a member of some group, category, or organization: as a.: a person having access to confidential information because of his position b.: an officer or a director of a company or a beneficial owner of 10 percent or more of an equity security registered on an exchange < laws regulating the manipulation of a company's securities by insiders >