approacher

Someone or something that approaches.

The monkeys’ calls warn other animals of approachers.

1589, Paul Ive (translator), Instructions for the Warres by Raimond Beccarie de Pavie, Seigneur de Fourquevaux, London: Thomas Man and Toby Cooke, Chapter 5, p. 38, […] houses or other thing standing néere vnto a towne, or fort, are meanes to surprise and approach vnto it, and the approacher not be discouered, or impeached by the defenders.

An asteroid on a near-Earth trajectory.

Extensive upgrades to the Arecibo antenna will be completed this spring, providing dozens of Toutatis-quality detections per year, spacecraft-quality images of the closest approachers, and hundred-pixel images of dozens of main-belt asteroids ( 9 ).

We have some close approachers," he says, "but not one that would have an impact trajectory."