Vaccines in French

The fifth entry is le vaccin à vecteur viral, and the middle word looks like a term of art when it is in fact the plainest thing in the phrase. Latin vehere meant to carry, and its agent noun was vector, the one that carries. That is the whole of it: le vecteur and our own « vector » are a carrier and nothing more. What makes the word hard to hear plainly is where English has since put it. « Vector » belongs to the mathematics classroom, where it is an arrow with a length and a direction, and to public health, where it is the mosquito that brings the disease rather than the disease itself; both senses are loud enough that the vaccine sense reads as jargon borrowed from one of them. It is the other way round, and all three are the same plain word. Older than any of them, the same root lies under a few English words with no Latin about them at all — « way », « wagon » and « weigh », the last of which meant to carry before it meant to measure. So the entry names a vaccine whose instructions arrive in a borrowed cart.