The 2 reasons why 'inflammable' mean the opposite of what it means

If you buy a polyester shirt advertised as “inflammable,” should you charge boldly into burning buildings or make sure to keep an extra safe distance from smokers and candle enthusiasts?

Ironically, many words in English reference the phenomenon of single words with multiple, contradictory meanings. Auto-antonym, contronym, antagonym, Janus word, enantidrome, antilogy, enantiosemy, antilogy... the list goes on. They all describe homographs (words with a particular spelling) with antonymous definitions.

Imagine I’ve invited you over to my house during the holiday season. Just before you arrive, I tell you that the tree has been trimmed and I’ve dusted the whole house. Excited for the homey atmosphere, you walk in, only to find a stubby, barren tree and a layer of fingerprint dust covering the walls and tabletops. “Sorry about the mess; I tried to warn you. I intend to catch whoever mutilated my tree!” I explain.

How do these misunderstandings happen? There are two distinct ways for a word to become its opposite.

1. POLYSEMY

Some words simply develop contradictory meanings over time. The verb sanction, for example, originally meant “to validate” or “to permit with authority.” The antonymous meaning “to impose a penalty on” arose in the last century out of a specific legal application of the word.

Often the process of verbing a noun will produce opposite senses. Seed, root, lease, and rent are all ambiguous for that reason. I can seed an apple and seed a garden with the same seeds I just removed. If you lease your car to me, I am the one leasing it!

Other words retain their grammatical form but take on new meanings when they jump between countries. Tabling a bill, for example, means “putting it up for debate” in Britain and “postponing it indefinitely” in the US.

2. CHANCE

Some words that seem the same because they’re spelled the same... aren’t! Fascinatingly, these “true homographs” are actually totally distinct words whose forms happen to overlap. Cleave, for example, which means both “to stick to” and “to divide,” comes from two different words in Old English that used to have distinct spellings and pronunciations. Somewhere in the last millennium, clēofan and clifian merged into one ambiguous word.

Can you think of auto-antonyms in other languages? Do these ambiguous words enrich or weaken communication