I teach English. After the false friends post some of you seemed to enjoy, here is another strange corner of the language: contronyms. Words that are their own antonym.
The wild part is that most native speakers have no idea these exist, and they cause genuine confusion in legal and business writing.
Some of my favourites:
Dust: to remove fine particles (dust the shelf) OR to add them (dust a cake with sugar).
Sanction: to approve (the board sanctioned it) OR to punish (economic sanctions). This one causes real ambiguity in headlines.
Cleave: to split apart (cleave the wood) OR to stick together (cleave to your beliefs). These actually come from two different Old English words that happened to merge into the same spelling.
Left: departed (he left) OR remaining (two slices left).
Oversight: careful supervision (regulatory oversight) OR a careless mistake (a costly oversight).
Bolt: to secure (bolt the door) OR to flee (the horse bolted).
Screen: to show (screen a film) OR to hide (a screen conceals).
Off: deactivated (turn it off) OR activated (the alarm went off).
Wind up: to start (wind up a toy) OR to finish (wind up the meeting).
A few reasons these happen: sometimes two unrelated words merged into one spelling (cleave), sometimes a neutral word drifted both ways (sanction), and sometimes the meaning flips depending on whose side you are on (to rent: the tenant rents, the landlord rents out).
The thing I find interesting as a teacher: you can know every word in a sentence and still misread it. The meaning of a contronym lives entirely in the context, not the word. Which is a good reminder that fluency is not about memorizing definitions. It is about reading the situation.
Reference:- Reddit