Meaning

adjective dignified and somber in manner or character and committed to keeping promises

adjective characterized by a firm and humorless belief in the validity of your opinions

originFrom Middle English solempne, solemne (“performed with religious ceremony or reverence; devoted to religious observances, sacred; ceremonious, formal; of a vow: made under a religious sanction, binding; religious celebration, celebration of a feast day; famous, well-known; important; grand, imposing; awe-inspiring, impressive; grave, serious; dignified; enunciated or held formally”) [and other…

Etymology from Wiktionary, CC BY-SA 3.0