informer

n person who informs, esp against a criminal or fugitive 告密者, 告发者, 检举人（尤指告发罪犯或逃犯的）.

inflexibility, inflexible, inflexibly, inflict, infliction, inflorescence, inflow, influence, influence on, influential, influenza, influx, inform, informal, informality, informally, informant, information, informative, informed, infra, infra dig, infra-, infra-red, infraction, infrared, infrastructure, infrequency, infrequent, infrequently, infringe, infringement, infuriate, infuriating, infuriatingly, infuse, infusion, ingenious, ingeniously, ingenue,