Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
informant, informer (nn.)
Informant’s general sense is “someone who provides information”: I just learned the news yesterday; my informant was my sister. Its specialized sense is “someone working for a researcher in societal topics or in language, someone who has information or experience the researcher needs”: While he was working on the tribal dialects, he used three elderly female informants. Informer is usually a pejorative term, meaning “a person paid to give information, particularly someone paid to reveal inside information about people and affairs in a group to which he or she belongs,” hence “a traitor.”
