Where does “bra-ket” come from?

bra-ket (English) comes from English bracket, from English bragget, from Middle English bragot, from Middle Welsh bragod, from Middle Welsh brag — malt.

bra-ket (English): The scalar product of two vectors (and optionally an operator), in Hilbert space, where the left (row) vector is a bra and the right (column) vector is a ket. Symbolised by ⟨...|...⟩ (bra and ket only) or ⟨...|...|...⟩ (bra, operator, ket)

Definitions

  1. The scalar product of two vectors (and optionally an operator), in Hilbert space, where the left (row) vector is a bra and the right (column) vector is a ket. Symbolised by ⟨...|...⟩ (bra and ket only) or ⟨...|...|...⟩ (bra, operator, ket)

Ancestry of “bra-ket”, step by step

StepLanguageWordMeaning
1EnglishbracketA fixture attached to a wall to hold up a shelf;...
2EnglishbraggetA liquor made of fermented ale and honey with...
3Middle Englishbragotbragget
4Middle Welshbragod—
5Middle Welshbragmalt
Every word from Middle Welsh brag →Every word from Middle Welsh bragod →Every word from Middle English bragot →
bra-ket — Etymology, Origin & Word History | Etymology Explorer