A continuous flow of air, or a current of air that moves steadily in one direction.
From 'air' plus 'stream' (Old English strēam, from Proto-Germanic *straumaz). The compound became common in aviation and meteorology contexts in the 20th century.
The jet stream is an 'airstream' of air moving 200+ mph at high altitude that shapes weather patterns across entire continents—ancient peoples couldn't see it but they felt its effects through unpredictable storms.
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