Other forms: blustering, blusters
To bluster is to talk loudly and aggressively with little behind it. Bluster and threaten, all bluster, blustering about it.
The emptiness is the whole charge — calling a threat bluster says it will not be carried out, which is a judgement and sometimes a mistaken one. Of wind it means blowing in violent gusts, which is the older sense and where the metaphor comes from. Note blustery.
1verbblusterTo talk loudly and aggressively with little behind it.
“The manager blustered about suing everyone, but he never did.”
2verbblowTo blow in violent gusts.
“The wind blustered around the house all night, rattling the windows.”
bluster is empty loud talk.
Middle English blusteren meant to wander about, and took the sense of blowing violently from Low German. Blow is a relative.
Middle Low German
blüstren
Middle English
blusteren — to wander about aimlessly
English, today
bluster
From Middle English blusteren (“to wander about aimlessly”); however, apparently picking up the modern sense from Middle Low German blüstren “to blow violently”; compare later Low German blustern, blistern. Related to blow, blast. Compare also stq bloasje (“to blow”), bruusje (“to bluster”).
Etymology from Wiktionary, CC BY-SA