This is not easy to explain (the reason why it has happened), whoever started it wants shooting!
Normally when we add a prefix (letters infront of the main word), it changes the meaning.
e.g.
polite - to be nice. im+polite - not nice.
Easy yes? so we would think, look at these words;
"flammable" - something that can easily catch fire.
"habitable" - a place that people can live in.
"valuable" - something is worth a lot of money or really important.
Pretty straight forward so far, but what happens when we add the prefix "in" .
"in+flammable" - "inflammable" = something that can easily catch fire. 🤔
"Careful! That liquid is flammable/inflammable" 🤬
"in+habitable" - "inhabitable" = a place that people can live in. 🤔
"After a lot of work, the house is finally habitable/inhabitable" 🤬
(This one is a little different in meaning but still gets confused) 🤔
"valuable" = "My watch is very valuable" 👌
"in+valuable" - "invaluable" (something is so valuable) - We can't put a price on it. 🙂
"His advice was invaluable for me in my career" 👍