1726, "make broad;" 1727, "grow broad;" from broad (adj.) + -en (1). The word seems no older than this (it was cited by Johnson in one of James Thomson's "Seasons" poems); broadened also is first found in the same poet. Broadening is recorded from 1835 as a noun, 1850 as a present-participle adjective.
updated on August 24, 2017