OK – these are not two different spellings of the same word, but two completely different and unconnected ones.

English: Weather satellite

Stationary (adjective) means not moving and can refer to just about anything. For example, communications and weather satellites are often in stationary orbits around the earth, so that the base-stations they communicate with do not have to track them across the sky. Looked at from earth, the satellites appear to be stationary or fixed in position.

Stationery (noun) is the kind of things needed for writing letters. It includes writing or copy paper, envelopes, pens, pencils, paper clips, files, rulers etc. The term ‘office supplies’ includes stationery, but is a broader term including office machines.

English: Stationery Store in North Street

English: Stationery Store in North Street (Photo credit: Wikipedia)