In historical linguistics, cognates or lexical cognates are sets of words in different languages that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical effects on both the sound and the meaning of a word, cognates may not be obvious, and often it takes rigorous study of historical sources and the application of the comparative method to establish whether lexemes are cognate or not. Cognates are distinguished from loanwords, where a word has been borrowed from another language.