IPA: /ˈtrɛdər/
KK: /ˈtrɛdər/
A person or thing that steps or walks on a surface, especially in a specific manner or for a particular purpose.
The treader carefully made their way across the muddy field.
Treader → It is formed from "tread" (from Old English *tredan*, meaning to step or walk) and "-er" (meaning a person who). A treader is a person who steps or walks in a particular manner or place.
Think of someone who is 'stepping' ('tread') — the '-er' indicates that this person is doing the action. A treader is simply someone who walks or steps.