- informant (n.) 1660s, "someone or something that supplies information," from L. informantem (nom. informans), prp. of informare (see INFORM (Cf. inform)). Meaning "one who gives information to the authorities, informer" is from 1783. As an adjective from 1890. The older noun was INFORMER (Cf. informer).
Etymology dictionary. 2014.