A bromide is a phrase or platitude that, having been employed excessively, suggests insincerity or a lack of originality in the speaker employing it.

The term "bromide" derives from the antiquated use of certain bromide

Bromide

A bromide is a chemical compound containing bromide ion, that is bromine atom with effective charge of −1. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.-Natural occurrence:...

 salts in medicine as mild tranquilizers and sedative

Sedative

A sedative or tranquilizer is a substance that induces sedation by reducing irritability or excitement....

s. Administration of a "bromide" (such as the original Bromo-Seltzer

Bromo-Seltzer

Bromo-Seltzer , is an antacid used to relieve pain occurring together with heartburn, upset stomach, or acid indigestion. Originally produced by inventor Isaac E...

prior to 1975 in the U.S.) would relieve anxiety and make the patient drowsy. Describing a phrase as a "bromide" is meant to humorously imply that it is a boring statement with similar soporific properties.