Cognates are best described as:

Cognates are best described as words in different languages that share the same root. This means that they have a common origin and often exhibit similar meanings, although they may not always be exact. For example, the English word "mother" and the Spanish word "madre" are cognates, both deriving from a common Proto-Indo-European root. Recognizing cognates is particularly useful in language learning, as it helps learners make connections between languages and expand their vocabulary more effectively.

Other options present different concepts that do not align with the definition of cognates. Antonyms in different languages refer to words that have opposite meanings, which is not relevant to cognates. Words that sound similar but have different meanings describe homophones, while unique phrases in a single language do not involve a comparison across languages at all. Thus, the identification of cognates as shared-root words captures their essential characteristic.