I've been becoming increasingly aware of words between English and Spanish that look so alike that they seem like they must be translations, and even Google Translate provides them as such. However, looking at the definitions, they're different. Sometimes slightly, other times completely. Sometimes, when asking native speakers of either language, they can't come up with closer translations on hearing the differences.
For example, these are completely different:
Condescending: having or showing a feeling of patronizing superiority.
Condescendiente: tends to accommodate to the likes and wishes of others.
These have a slight but important difference:
Fallacy: The use of invalid or otherwise faulty reasoning, or "wrong moves" in the construction of an argument.
Falacia: False argument that appears true to trick or cause error.
(In other words, in Spanish it means it must be intentional while in English it doesn't).
Affectation: A show, pretense, or display. Behavior that is assumed rather than natural; artificiality.
Afectación: Something that affects.
I imagine definitions shift with the different usage in different cultures. As I notice these, I become increasingly uncertain that I'm using the words I know correctly, because I usually learn them in one language and then try to apply them in another by using common translation tricks ("tion" -> "ción", etc.). I often verify they exist, but hardly ever compare the definitions to ensure they match completely. I wish to search these like "common _ between English and Spanish" on Google, but I don't know what to call them.
EDIT: I just remembered a funny one. It had to be explained to me when I said "that's so exciting!" in spanish and everyone looked at me weird, seemingly wondering if I really meant what I said.
Exciting: causing great enthusiasm and eagerness.
Excitante: sexually arousing.
In my defense, on looking at the definitions online, both words mean both things, but the prevailing meaning in colloquial usage differs. They explained to me that I wanted to use the word "emocionante" which in English ("emotional") is not quite right.
These are called "false friends". Wikipedia:
False friends are words in two languages that look or sound similar, but differ significantly in meaning. An example is the English embarrassed and the Spanish embarazada (which means pregnant), or the word sensible, which means reasonable in English, but sensitive in French and Spanish.
(Nice when you meet someone who's both sensible and sensible, isn't it?!)
Interestingly enough, the article claims that the title originated from a book calling them the false friends of the hapless translator, not of each other, which is what I always assumed.
As the article notes, the phenomenon can be caused by actual cognates diverging semantically in the different languages, or from loanwords borrowed without all their applications (or an altered application), or from coincidental homonyms.
I use this term (as the French faux amis) with my students daily.