The sense of ‘favourable wind’ is etymologically older, attested in Classical Latin aura (cf. or²) and derived from Ancient Greek αυρα. From that, the sense ‘weather conditions’ or ‘atmosphere’ developed, already in Classical Latin. The chronologically secondary but much more common sense (both in Anglo-Norman and continental French) of ‘storm’ may have been attained, initially, through the use of adjectives such as grant, mal, malveis. The word seems to be used mainly (though not exclusively) in a nautical context.