- IPA: /kɛt/
Etymology 1 
- (physics) A vector, in Hilbert space, especially as representing the state of a quantum mechanical system; the complex conjugate of a bra; a ket vector. Symbolised by |...〉.
- A particular ket, say , might be represented by a particular column vector. Its corresponding bra, , 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 and Danish kjöd. 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.
ket (plural kets)
- (Northern England) Carrion; any filth.
- (Northumbrian) Sweetmeats.
- (Geordie) A sweet, treat or candy.
- The Collaborative International Dictionary of English v.0.48 on DICT.org
- Northumberland Words, English Dialect Society, R. Oliver Heslop, 1893–4
- A Dictionary of North East Dialect, Bill Griffiths, 2005, Northumbria University Press, ISBN 1904794165
- A List of words and phrases in everyday use by the natives of Hetton-le-Hole in the County of Durham, F.M.T.Palgrave, English Dialect Society vol.74, 1896, 
Etymology 3 
Usage notes 
Together with ne: ne ... ket. This is the same structure as French ne ... pas.
Alternative forms 
- (common) kjöt