A rosemary (a type of shrub) could easily be a combination of two women's names. Today, that is all it amounts to. In Middle English, rosemary used to be rosmarine. The change to the present word was likely influenced by folk etymology; someone somewhere looked at the word and decided that it was wrong, that it clearly was a portmanteau of "rose" and "Mary" and spelled it thus. However, we can already begin to glimpse the true etymology. Rosmarine is from the Latin word rosmarinus, which still meant "rosemary" but also meant "dew of the sea" in a poetic way. This definition was also literal in a semantic way: ros meant "dew" and marinus (with today's word marine descended from it through French marin) meant "of the sea". Marinus is clearly a conjugated form of the word mar ("the sea"), which is further reconstucted as having origins in the Proto-Indo-European word mori, "body of water". Ros, on the other hand, is directly from the PIE root ers, "to be wet". So rosemary really means "wet water". Interesting...!
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd