Bookbinding. four gathered sheets folded in two for binding together.
3.
Mathematics.
an expression of the form a + bi + cj + dk, where a,b,c, and d are real numbers; i^{2} = j^{2} = k^{2} = −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.
(maths) a generalized complex number consisting of four components, x = x0 + x1i + x2j + x3k, where x, x0…x3 are real numbers and i² = j² = k² = –1, ij = –ji = k, etc
(kwə-tûr'nē-ən) Any number of the form a + bi + cj + dk where a, b, c, and d are real numbers, ij = k, i^{2} = j^{2} = -1, and ij = -ji. Under addition and multiplication, quaternions have all the properties of a field, except that multiplication is not commutative.
a band of four soldiers. Peter was committed by Herod to the custody of four quaternions, i.e., one quaternion for each watch of the night (Acts 12:4). Thus every precaution was taken against his escape from prison. Two of each quaternion were in turn stationed at the door (12:6), and to two the apostle was chained according to Roman custom.