When you solemnize something, you make it serious or dignified. You might solemnize a meal by lighting candles and saying grace before you eat.
How much fun is it to get to pronounce a letter that is normally silent? You'll know when you wrap your tongue around this one, in which the n, normally silent in solemn, gets to introduce the suffix -ize. Even more fun is the fact that solemnize has a Greek suffix tacked onto a Latin root, sollemnis, or "formal, ceremonial, traditional." But we shouldn't be having so much fun with a verb whose meaning is "perform with dignity or gravity."