Vector Vec"tor, n. [L., a bearer, carrier. fr. vehere, vectum, to carry.] 1. Same as Radius vector. 2. (Math.) A directed quantity, as a straight line, a force, or a velocity. Vectors are said to be equal when their directions are the same their magnitudes equal. Cf. Scalar. Note: In a triangle, either side is the vector sum of the other two sides taken in proper order; the process finding the vector sum of two or more vectors is vector addition (see under Addition).