Definition from Wiktionary, the free dictionary
From Middle English solemne, from Old French solempne, from Late Latin sōlennis and sōlempnis, from Latin sōlemnis, from sollemnis (“ritual; festive, solemn, customary, celebrated at a fixed date”), from sollus (“entire”).
- Deeply serious and somber.
- Somberly impressive.
- Performed with great ceremony.
- Gloomy or sombre.
Derived terms 
deeply serious and somber
performed with great ceremony
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From Latin sollemnis.