/ səˈlemnəti; NAmE / noun
1.
[ U ] the quality of being solemn :
He was smiling, but his eyes retained a look of solemnity.
He was buried with great pomp and solemnity.
2.
solemnities [ pl. ] ( formal ) formal things that people do at a serious event or occasion :
to observe the solemnities of the occasion
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WORD ORIGIN
Middle English (in the sense observance of formality and ceremony , frequently in the phrases in solemnity , with solemnity ): from Old French solemnite , from Latin sollemnitas , from sollemnis customary, celebrated at a fixed date, from sollus entire.