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mid-15c., "act of celebrating," from Old French solemnisation, solempnisation, or directly from Medieval Latin solempnizationem (nominative solempnizatio), from Latin sollemnis (see solemn).
late 14c., "honor by ceremonies," from Old French solemnisier, from Medieval Latin solemnizare, from Latin solemnis (see solemn). Meaning "render solemn" is from 1726. Related: Solemnized; solemnizing.