ket

Etymology 1

From bra-ket notation invented by Paul Dirac, from bracket.

noun

1. (physics) A column vector, in Hilbert space, especially as representing the state of a quantum mechanical system; the complex conjugate of a bra (a row vector); a ket vector. Symbolised by |...〉.
   A particular ket, say |A⟩, might be represented by a particular column vector. Its corresponding bra, ⟨A|, would then be represented by the row vector which is the transpose conjugate of that column vector.

Etymology 2

Compare Icelandic kjöt (“flesh”); akin to Swedish kött, Danish kød, and Norwegian kjøtt. The use of the term ket for "candy" or "sweets" probably derived from its use to describe sweet meats or as a deterrent to children.

noun

1. (Northern England) Carrion; any filth.
2. (Northumbria) Sweetmeats.
3. (Wearside) A sweet, treat or candy.

Etymology 3

Clipping of ketamine.

noun

1. (colloquial) ketamine

Etymology 4

noun

1. (Scotland) matted wool