IPA: /ɪkˈstrævəɡənsi/
KK: /ɛkˈstrævəɡənsi/
A quality or state of being extravagant, often involving excessive spending or behavior that goes beyond what is reasonable or necessary.
Her extravagancy was evident in the lavish parties she threw every month.
Extravagancy is formed from "extra-" (meaning outside or beyond) and "vagari" (meaning to wander). The word describes a state of wandering beyond the usual limits, often referring to excessive or wasteful behavior.
Think of going 'beyond' ('extra-') the usual limits and 'wandering' ('vagari') into excess — that's why extravagancy means excessive behavior.