To talk in a loud, aggressive, or threatening way to intimidate, or empty boastful talk with no real substance.
Possibly from Old Norse 'blustre' or Low German 'bluster'. The word may be imitative of wind sounds, which later extended to describe loud, aggressive human speech that produces a lot of noise but little action.
Bluster originally meant a strong wind, and people who talk big without backing it up literally produce a lot of hot air—making the word a perfect metaphor for empty aggression!
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