Lightness of mood or lack of seriousness; the quality of not taking things too seriously.
From Latin 'levitas' (lightness, from levis meaning light). The physical sense of being light came first, but by the 1600s it was used metaphorically for light-hearted or non-serious attitudes.
The word 'levity' and 'gravity' are opposites in both physics (one is light, one is heavy) and personality, and that's not random—medieval scholars used the same metaphor to say serious people are 'weighed down' while funny people 'float away.'
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