Synonyms of the word 
LIGHTHEARTEDNESS → BLITHENESS - CAREFREENESS - CHEERFULNESS - INSOUCIANCE - LIGHTSOMENESS
lightheartedness
- n. (uncountable) The property of being lighthearted, joyous, cheerful, without a care.
- n. (countable) An amusement or item of a pleasant but inconsequential nature.
blitheness
- n. The characteristic of being blithe.
carefreeness
- n. The property of being lighthearted, joyous, cheerful, without a care.
cheerfulness
- n. The state of being cheerful; joy.
insouciance
- n. carelessness, heedlessness, indifference, or casual unconcern.
- n. nonchalance.
lightsomeness
- n. (archaic) The quality of being lightsome.
If you are interested in words, visit the following sites :
- wiktionary.org/lightheartedness For complete definition of a word
- 1word.ws/lightheartedness to play with words, suffixs, prefixs, etc.