The Collaborative International Dictionary of English v.0.48:

Bromide \Bro"mide\, 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] Bromide paper

WordNet (r) 3.0 (2006):

bromide
    n 1: any of the salts of hydrobromic acid; formerly used as a
         sedative but now generally replaced by safer drugs
    2: a trite or obvious remark [syn: platitude, cliche,
       banality, commonplace, bromide]