Definition of platitudinarian in US English:

platitudinarian

adjective

  • Characterized by platitude; tending to use platitudes.

noun

  • A person who utters or deals in platitudes.

Origin

Mid 19th century; earliest use found in Thomas Lynch (1818–1871), hymn writer and composer. From platitude + -in- + -arian, after e.g. latitudinarian, latitudinarian. With use as adjective compare slightly earlier platitudinary.