insider

Meanings

1. 1
   noun

   A person who has special knowledge about the inner workings of a group, organization, or institution.

   Near-synonyms: initiate, old hand, habitué

2. 2
   noun

   A person who is within an enclosed space.

   To the insider, the ceiling is like a small firmament twinkling with astral radiations.

3. 3
   noun

   an officer of a corporation or others who have access to private information about the corporation's operations

Etymology

From inside + -er.