informer
Word family (noun) informant information informer misinformation disinformation (adjective) informative ≠ uninformative informed ≠ uninformed (verb) inform misinform (adverb) informatively
From Longman Dictionary of Contemporary Englishinformerin‧form‧er /ɪnˈfɔːmə $ -ɔːrmər/ noun [countable] TELLsomeone who secretly tells the police, the army etc about criminal activities, especially for money SYN informant