From Middle English quaternioun, from Late Latin quaterniō, from quaternī + -iō, from quater ("four times").

The mathematics sense was .

• (British) IPA: /kwəˈtɜːni.ən/
• (America) IPA: /kwɑˈtɜɹniɑn/, /kwə-/, /-ən/

quaternion (plural quaternions)

1. A group or set of four people or things.
   • 1526, [William Tyndale, transl.], The Newe Testamẽt […] (Tyndale Bible), [Worms, Germany: Peter Schöffer], →OCLC ↗, Acts xij:[3], folio clxxj, verso ↗:

     Then wer the dayes of unlevended breed, and when he had caught hym, he put him in preson, and delyvered hym to iiij. quaternions off soudiers to be kepte, entendynge after ester to brynge hym forth to the people.

2. A word of four syllables.
3. (mathematics) A type of four-dimensional hypercomplex number consisting of a real part and three imaginary parts (real multiples of distinct, independent square roots of −1 denoted by i, j and k); commonly used in vector mathematics and as an alternative to matrix algebra in calculating the rotation of three-dimensional objects.

• (group of four) foursome, tetrad; see also Thesaurus:quartet

• French: quaternion
• German: Quaternion
• Italian: quaternione
• Portuguese: quaternião
• Russian: кватернион
• Spanish: cuaternión