the.com/informer

means Someone who secretly tells authorities about others' wrongdoing, usually for money, protection, or to save their own skin.

from Straightforward Latin lineage: 'informare' meant to give shape or form to something, and by extension, to shape an idea in someone's mind — to instruct or describe. 'Informer' entered English via French in that same sense of 'one who tells, who shapes understanding.' Over centuries the word narrowed and darkened: telling authorities what you know about a crime became its dominant, specialized use, especially once it picked up legal and criminal-underworld connotations. The 'snitch' sense isn't a twist of meaning so much as the original 'one who informs' settling into its most loaded, least neutral job.