I answered it while in the stacks one morning, and an older woman asks:
Patron: Can I ask you the definition of a word?
Me: Sure [as I scurry back to the desk and the safety of our ready-reference and access to an online spell checker]
Patron: Good, thank you, it's spelled l-o-c-as-in-cat-a-v-as-
Me: [just arriving at the desk and trying to write the word out] I'm sorry, did you say B as in boy?
Patron: -in-victory-o-r-e-as-in-easter. No, an E not a P
This actually went on for some time, and by the time I was sure I had the right spelling, I had so many scribbles and crossings-out on my scrap paper that I didn't recognize the word. I said I'd check the dictionary, and the patron said she'd already checked two dictionaries and couldn't find it.
So while I was looking it up, I asked her where she'd seen the word. She said it was in the caption to a photograph in the newspaper. I didn't see it in my dictionary either, so typed it into Google.
Even as I was typing l-o-c-a-v-o-r-e, it didn't dawn on me what it was until I saw the search results.
When I explained to her that, just as a herbivore eats only plants, a locavore is a person that eats only local food, she was delighted - both to learn a new word, and also that a made-up word would appear in the newspaper.
Having a cordless phone is nice, but maybe I should try to talk the library into getting iPhones so that we can answer questions like this in the stacks without having to rush back to the desk - sort of roving reference in a holster.