bromide

n. 1. (Chem.) A compound of bromine with a positive radical. [ 1913 Webster ]

2. A person who is conventional and commonplace in his habits of thought and conversation. [ Slang ] [ Webster 1913 Suppl. ]

The bromide conforms to everything sanctioned by the majority, and may be depended upon to be trite, banal, and arbitrary. Gelett Burgess. [ Webster 1913 Suppl. ]

3. a conventional or trite saying; -- often used in the phrase “old bromide”. [ PJC ]