I recently made the connection that typhus and typhoid are different diseases. The latter was more recently discovered; it was thought to be a variant of typhus, so they just added the suffix -oid (used to denote resemblance) and that was that. Typhus comes from the Ancient Greek word typhos, which meant "smoke"; the term was used by Hippocrates to describe conditions of stupor, and people later on thought that, since the affliction could cause feelings of drowsiness, it was an appropriate moniker. Typhos is from typhein, an earlier verb meaning "to smoke". That's thought to be from the Proto-Indo-European reconstruction dheu, which meant "dust" or "vapor" but also had connotations of sensory confusion that led to the development of words such as deaf and typhoon.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.