red herring Definition

red herring
noun

1. A herring which has been cured and smoked to a dark reddish colour.
2. A subject, idea, clue, etc introduced into a discussion, investigation, etc to divert attention from the real issue or to mislead.

Etymology: 19c in sense 2, from the fact that a red herring drawn across a track would put a dog off the scent; 15c in sense 1.