means A quantity that has both a magnitude and a direction — or, in biology and computing, the thing that carries something (a disease, a gene, a payload) from one place to another.

from From Latin vector, "a carrier, conveyer, one who bears," from vehere, "to carry or convey" — the same root that rolls underneath vehicle. So the word literally means "the one that carries," which is why a mosquito (carrying disease) and an arrow (carrying direction and force) earn the same name. Mathematics borrowed it in the 19th century for quantities pointing somewhere with a definite push; biology took the carrier sense more literally.