a person who goes ahead and makes known the approach of another; herald.

anything that foreshadows a future event; omen; sign

Frost is a harbinger of winter.

a person sent in advance of troops, a royal train, etc., to provide or secure lodgings and other accommodations.

to act as harbinger to; herald the coming of.

noun

augury , forerunner , foretoken , herald , messenger , omen , portent , precursor , sign , signalnotes:a harbinger is an indication of the approach of something or someone; a messenger is a person who carries a communications or performs an errand; an omen is a sign of something about to happen , foreshadower , presager , angel , indication , presage , shelter , signal , symbol , usher