One little letter is all that separates stationary and stationery, two words with the same pronunciation but very different meanings.
Stationary is an adjective that means not moving:
Because Max knew the pyramids of Egypt to be stationary, he realized he was hallucinating.
The Bride of Frankenstein will not be roaming the village today, for she has pledged to remain stationary.
To reduce the need to repair potholes, the city bought a fleet of stationary buses.
Stationery is a noun that means writing materials:
I make a certain impression when I write letters using My Little Pony stationery.
What stationery would you recommend for death threats and ransom notes?
The epistolary outdoorsman hiked into the wilderness with only his backpack, canteen, hunting knife and vellum stationery.
Mnemonic device: When you’re referring to letter and paper, match the er in those words with the er in stationery.