“Legerity” developed from the French word “légèreté,” which means “thoughtlessness,” but in English, the word implies a sense of quick-wittedness or nimbleness. While it is good to be lighthearted, it is important to have legerity and pay attention to the time, place, and occasion. If you are too jocund, ebullient, blithe, effervescent, genial, mirthful, or diverting (all synonyms for “lighthearted”) in the wrong situation, you might be considered thoughtless.