These two words sound the same, but mean very different things. Perhaps this post will help you remember which is which…
‘Stationery’ means things that you might write or draw with. These were often bought by people who were off on a journey so they could fill in a crossword, write a letter or postcard, or make notes for their business meeting, before the age of Instagram.
The shops that sold stationery were often in train stations – those shops were called ‘stationers’, and so the articles of writing equipment they sold were termed ‘stationery’.
The other word, ‘stationary’, means to remain still and unmoving, like a bus or train would be in a station.
So, you can say, “I bought some stationery at the stationers, while the train was stationary at the station”. But you’re more likely to say, “I bought a Happy Meal in Maccy D’s while the train was three hours delayed, due to vandalism north of Luton, but it had gone cold by the time I’d taken an Instagram of it that I was happy with, so I bought another one. Mental!”