vector

Vector in Latin means a carrier, a transporter, from vehere (to carry, to convey), from PIE *weǵh- (to go, to transport). The word entered English through several technical disciplines at different times, always carrying something. In astronomy, William Rowan Hamilton used 'vector' in 1843 for a quantity with both magnitude and direction, contrasting it with 'scalar' (magnitude only). Hamilton was working on quaternions, a mathematical system for describing rotations in three-dimensional space.

The mathematical vector became fundamental to physics. James Clerk Maxwell's electromagnetic equations (1865) required vectors — electric and magnetic fields have direction as well as strength. Every force in physics is a vector. Velocity is a vector (speed plus direction). Acceleration is a vector. Without the concept of a carrier — a quantity that transports information about both how much and which way — modern physics would be impossible.

The epidemiological meaning appeared in the late nineteenth century. A disease vector is an organism that carries a pathogen from one host to another — a mosquito carrying malaria, a flea carrying plague, a tick carrying Lyme disease. Ronald Ross identified the mosquito as the vector for malaria in 1897 and won the Nobel Prize for it. The Latin carrier carried disease as naturally as it carried direction.

Computer science added another meaning. A vector in programming is an ordered list of values — an array. This usage, emerging in the 1950s, draws on the mathematical meaning: a vector is a collection of numbers arranged in a specific order, carrying structured information. The word now works in mathematics, physics, biology, medicine, and computer science, always carrying something from one place to another.