raison d'etre

English Thesaurus

1. the purpose that justifies a thing's existence (noun.attribute)

hypernym	:	function, purpose, role, use,
definition	:	what something is used for (noun.attribute)

2. reason for being (noun.cognition)

hypernym	:	rationalisation, rationalization,
definition	:	the cognitive process of making something seem consistent with or based on reason (noun.cognition)