busybody

Short definition from Wiktionary

Noun

1. 1
   Someone who interferes with others; one who is nosy, intrusive or meddlesome.
2. 2
   A device consisting of three mirrors that, when attached to the wall of a house, allows an occupant to see who is at the front door without a direct line of sight.

Verb

1. 1
   To meddle or interfere.