Stationary and stationery are just one letter off, but that seemingly small difference changes the meaning of these words entirely. These two terms share the Latin root statiōnārius, which derives from the word station meaning “a standing place.”
Stationary with an a is the older of these two terms, and it means “fixed in one place and not moving,” like a stationary bicycle at the gym. Stationery with an e stems from the term stationer, which refers to “a person who sells the materials used in writing, such as paper, pens, pencils, and ink.” Though now archaic, stationer also used to refer to to a bookseller or publisher. Stationery eventually came to mean the things a stationer sold, though stationeries are a rare sight these days, when receiving snail mail from a friend is a special occasion.
How do you remember the difference? One way is to remember that a stands for adjective. So when you see stationary with an a, you’ll know that it is an adjective and as such it must describe something or someone. Stationery is a noun. Another mnemonic to help you is: let the a near the end of stationary remind you of “at rest” and the e near the end of stationery stand for “envelope.”