means A person or system that carries information, messages, or parcels from one party to another.

from From the Old French 'messagier,' built on 'message' — itself from Latin 'missus,' the past participle of 'mittere,' meaning 'to send.' The intrusive 'n' (giving us 'messeNger' rather than 'messager') is a quirk of English habit, the same itch that turned 'passager' into 'passenger' and 'harbinger' from earlier 'harbergere.' At root, then, a messenger is simply 'one who has been sent.'