In linguistics, cognates are words that have a common etymological origin. This learned term derives from the Latin cognatus (blood relative). Cognates within the same language are called doublets. Strictly speaking, loanwords from another language are not considered cognates.
For example, the English words shirt and skirt are doublets.
Cognates do not need to have the same meaning, which may have changed as the languages developed separately. For example, consider English starve and Dutch sterven or German sterben (“to die”); these three words all derive from the same Proto-Germanic root, *sterƀ- (“die”). English dish and German Tisch (“table”), with their flat surfaces, both come from Latin discus, but it would be a mistake to identify their later meanings.