Dictionary.com Word FAQs
Where did the word flagstone come from?
There is no connection between this word and cloth flags. The flag in flagstone is from the Norse word flaga 'slab of stone' as a flagstone is a hard fine-grained stone split ('flaked') into flat pieces suitable for paving. There are other words whose names are similarly misleading: there is no butter in buttermilk, egg in eggplant, worms or wood in wormwood, pine or apple in pineapple, or ham in hamburger. In the case of flagstone, our misunderstanding comes from not knowing this variant meaning of flag.