A person who gives information to authorities about another person's illegal activities, often secretly.
From Old French 'informer' (to inform), combining Latin 'in-' (in/into) and 'formare' (to form/shape), originally meaning to give form or shape to understanding.
The original sense of 'inform' meant to shape someone's mind with knowledge—informers literally shape the mind of authorities by giving them knowledge about crimes.
Complete word intelligence in one call. Free tier — 50 lookups/day.