False cognates are more commonly known false friends.
False friends are words in two languages that look or sound similar, but have quite different meanings.
Here are a few examples from the situation of a native English speaker learning Spinish:
(I) embarazada ≠ embarrassed.
It is so prevalent because we all at some point want to say we are “embarrassed” to speak Spanish. But don’t use the word embarazada to express that sentiment. Embarazada means pregnant, which has nothing to do with what you mean to say. If you want to express embarrassment, the correct word is avergonzada.
(II) constipado ≠ constipated.
The first time you hear the word you might feel like you’ve just been given a little TMI (too much information), but constipado actually refers to having a cold, a synonym of the Spanish word resfriado. If you really want to talk about your bowel movements (though not recommended) the word you want is estreñido.
(III) molestar ≠ molest
When you first hear this word you may feel a bit shocked if you’re thinking it means the same in English. But molestar in Spanish means to bother. You will often hear it as a form of politeness as in “No quiero molestarte, pero tienes algunos minutos” meaning ” I don’t want to bother you, but do you have a few minutes”.
(IV) libreria ≠ library
Una libreria has books, but they are books for buying, as in a bookstore. If you want to go to the library, you are looking for the biblioteca, where the books are free to rent and you can study.
(V) sensible ≠ sensible
It’s almost cruel because they are even spelled the same, but sensible does not mean someone who is sensible or reasonable. It means someone who is sensitive, as in reacting with emotion. If someone is sensible, we would say she was sensato or razonable.