extravagant: [14] An extravagant person is literally one who ‘wanders out of’ the proper course. The word comes from the present participle of medieval Latin extrāvagārī, a compound formed from the prefix extrā- ‘outside’ and vagārī ‘wander’ (source of English vagabond, vagary, and vagrant), which seems originally to have been used adjectivally with reference to certain uncodified or ‘stray’ papal decrees. This was the word’s original application in English, and the present-day meanings ‘wildly excessive’ and ‘spending too lavishly’ did not really establish themselves before the early 18th century. => vagabond, vagary, vagrant
extravagant (adj.)
late 14c., from Medieval Latin extravagantem (nominative extravagans), originally a word in Canon Law for uncodified papal decrees, present participle of extravagari "wander outside or beyond," from Latin extra "outside of" (see extra-) + vagari "wander, roam" (see vague). Extended sense of "excessive, extreme, exceeding reasonable limits" first recorded 1590s, probably via French; that of "wasteful, lavish, exceeding prudence in expenditure" is from 1711. Related: Extravagantly. Wordsworth ("Prelude") used extravagate (v.).