Abeam

adv. on a 90 degree angle to the keel of a ship (Nautical)

Adverb
1. at right angles to the length of a ship or airplane

(adv.)
On the beam, that is, on a line which forms a right angle with the ship's keel; opposite to the center of the ship's side.
  

An aircraft is "abeam" a fix, point, or object when that fix, point, or object is approximately 90 degrees to the right or left of the aircraft track. Abeam indicates a general position rather than a precise point. (FAA4)

Bearing approximately 090 or 270 degrees relative; at right angles to the longitudinal axis of a vehicle. 18/08/98

Gisement voisin de 090 ou 270 . C'est-à-dire: direction sensiblement perpendiculaire à l'axe longitudinal d'un élément mobile. 1/2/73