Using stationary and stationery provides the English language with another opportunity to trip up the unwary.
Stationary means something is not moving; it’s still. For example:
The car is stationary.
The train gradually slowed, until it was stationary.
Stationery refers to the things you have hanging about in your office—envelopes, writing paper etc. For example:
We never have enough stationery in the office.
Shopping for stationery is one of my favourite pastimes.
How do you remember the difference?
Remember that envelopes start with an E, and stationery, with an E, includes envelopes. If you write that your car is stationery, you’re telling the world it’s made of paper, envelopes and paper clips. That’s a possibility of course, particularly if you have a vintage car made by British Leyland in the 1970s, but it’s unlikely.