CATTLE DOCTOR

In 1646, English polymath Sir Thomas Browne published a rather interesting book entitled Pseudodoxia epidemica, in which he essentially dispelled fake news, correcting common superstitions and errors of the time. The third part of the seven-section tome  dealt with animals, and in it he wrote one sentence about how even veterinarians believe that horses don't have gallbladders. That was the first use of the word veterinarian in the English language (replacing its bizarre predecessor dog-leech), and it only took off from there, now constituting about 0.00012% of all spoken words. Browne borrowed the word from Latin veterinarius, which meant "cattle doctor" (over time, that definition got widened to "animal doctor" in general), and that has an uncertain etymology. It could be from words meaning "old", "to draw", or something else, but we're not completely sure.