cynosure
I knew that a cynosure was a center of attention (I’ve almost always seen it in the phrase “the cynosure of all eyes”), and I knew that it was the name of a city in the comic book series Grimjack.
But I hadn’t known that it’s also a name for Ursa Minor or for the north star, according to my dictionary.
(At least I hadn’t known that ’til 2010, when I wrote a note to myself to post this. But I had forgotten it in the meantime. I suppose I ought to do a better job of really learning all these new-to-me words that I post, so that when I see them again years later they won’t again seem to be new.)