bra-ket
nounEtymology Concatenation of the terms bra and ket, which were introduced in 1939 and in turn derive from the splitting of the English word bracket.
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Natural sciences, Physical sciences, Physics 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).