Definition: In a technical sense, two words that have a common origin are cognates. Most often, cognates are words in two languages that have a common etymology and thus are similar or identical. For example, the English "kiosk" and the Spanish quiosco are cognates because they both come from the Turkish kosk.
Cognates often have a similar meaning, but in some cases the meaning has changed over the centuries in one language or another. An example of such a change is the English word "arena," which usually refers to a sports facility, and the Spanish arena, which usually means "sand." They both come from the Latin harena, which originally meant "sand" and came in time to also refer to an area of a Roman amphitheater that was covered with sand. Spanish retained the meaning of "sand" (although the word can sometimes refer to a sports arena), but English expanded the word's meaning to include facilities something like the Roman amphitheater.
In a popular and less technical sense, the term "cognate" also is used to refer to words in two languages that are similar but have no common origin, such as the Spanish sopa (meaning "soup") and the English "soap."
Also in a popular and not technical sense, the phrase "false cognate" is used to refer to cognates that have different meanings, such as the Spanish parar (to stop) and the English "pare" (to trim). A more precise term to use for such word pairs is "false friends."
Also known as: palabra afín, palabra relacionada or palabra cognada in Spanish
Examples: Cognate pairs with similar meanings number in the thousands and include "azure"/azul, "committee"/comité and "morphine"/morfina. Spanish cognates that are false friends include asistir (which usually means "to attend," not "to assist"), contestar (which usually means "to answer," not "to contest") and sano (which usually means "healthy" rather than "sane").