Stationary, with an a, is an adjective only. It means not moving or not capable of being moved. Stationery, with an e, is a noun only. It refers to writing paper and envelopes. In North America, it’s usually used in reference to paper and materials for writing letters. Outside North America, it’s used more broadly.
Though stationary and stationery are spelled almost alike, they have different origins. Stationary comes from the Latin stationarius, meaning belonging to a military station, while stationery comes from the Middle English noun staciouner, meaning bookseller.
After months of being criticized for remaining stationary in the polls, White House hopeful Mitt Romney is finally getting the surge he’s been waiting for. [Wall Street Journal]
City status affords no new rights, privileges or duties; the biggest change is in the signage and stationery. [Economist]
Last we checked, people who get hurt tobogganing tend to have collided with stationary objects: Trees, fences, cars. [National Post]
Poverty doesn’t stop after Christmas, especially for families facing a school year with new stationery, uniforms and fees. [Stuff.co.nz]