buoyancy

(noun) cheerfulness that bubbles to the surface. Synonyms: perkiness.

(noun) the property of something weightless and insubstantial. Synonyms: airiness.

(noun) the tendency to float in water or other liquid.

(noun) irrepressible liveliness and good spirit. Synonyms: irrepressibility. Example: "I admired his buoyancy and persistent good humor."