Stationary vs Stationery
Quick answer: Stationary with an A means standing still. Stationery with an E is paper, envelopes, and writing supplies.
Stationary
Adjective: not moving; fixed in place.
“The traffic was completely stationary.”
Stationery
Noun: writing paper and office supplies.
“She wrote the note on floral stationery.”
How to remember it
stationEry with an E is for Envelopes; stationAry with an A stAys put.
Common mistake
'Fancy stationary set' — paper products take the E.