- a group or set of four persons or things.
- four gathered sheets folded in two for binding together.
- Mathematics.
- an expression of the form a + bi + cj + dk, where a,b,c, and d are real numbers; i2 = j2 = k2 = −1; and ij = −ji = k, jk = −kj = i, and ki = −ik = j.
- a quantity or operator expressed as the sum of a real number and three complex numbers, equivalent to the quotient of two vectors. The field of quaternions is not commutative under multiplication.
- a generalized complex number consisting of four components, x = x 0 + x 1 i + x 2 j + x 3 k, where x, x 0 … x 3 are real numbers and i² = j² = k² = –1, ij = –ji = k, etc
- another word for quaternary (def. 5)
