The antonyms for larkiness are seriousness, solemnity, gravitas, and somberness. Larkiness refers to a playful, carefree attitude or sense of humor characterized by a willingness to engage in fun activities that are not necessarily productive or practical. In contrast, seriousness refers to a state of being grave or sober-minded, solemnity refers to a sense of dignity or formality, gravitas refers to seriousness and weightiness of manner or attitude, and somberness refers to a mood that is dark, gloomy, or melancholy. These antonyms reflect a variety of different attitudes and emotions that are less playful and more sober-minded, serious, and reflective.