solemnly. Use solemnly in a sentence. LINK / CITE ADD TO WORD LIST. adverb. Solemnly is defined as something done in a serious manner or in a way that reflects a ritual or tradition.An example of something that would be described as acting solemnly is how we all should behave at a funeral.olemnly. Use solemnly in a sentence. LINK / CITE ADD TO WORD LIST. adverb. Solemnly is defined as something done in a serious manner or in a way that reflects a ritual or tradition.