IPA: /ˈsteɪʃənər/
KK: /ˈsteɪʃənər/
A person or business that sells writing materials, paper, and office supplies.
I went to the stationer to buy some envelopes and pens.
Stationer → It is formed from "station" (from Latin "statio", meaning a standing place or position) and "-er" (meaning a person who). A stationer is a person who sells stationery or is involved in the business of writing materials.
Think of a 'standing place' ('station') where a person ('-er') sells writing materials. This helps you remember that a stationer is someone who provides stationery.