Stationary means fixed in one place or not moving, it can be used as an adverb or an adjective.
Stationery refers to material and supplies that is used in writing and in the schools and offices. Such as, pens, books, notepad, stapler etc. The person who sells stationery is called a stationer.
Stationery can also be used as a noun or an adjective.
You can remember the difference between these two words by remembering this little trick, let the 'a' in stationary stand for 'at rest' and let the 'e' in stationery stand for 'envelope'.
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