Why Does Vector Mean To Carry?

The word vector is used as a noun to convey the idea of an insect that is known to spread a disease; it carries a disease from one living being to the other. It is this reason that makes people use the word vector as a synonymous term for the word carry.
      
Though you can use the term to signify the above mentioned idea, you will seldom find people using the word in this context and whenever the word is being used it describe either a mathematical term or a course that an aircraft takes.
      
When you are using the term in the context of mathematics, it describes quantity that is known to have both size and direction. You can put forth the examples of acceleration and velocity as vectors as both of them are known to have size and direction.