I. adverb 1. on a line at right angles to a ship’s or an aircraft’s length. • the lighthouse was abeam at noon.
2. ( abeam of) — opposite the middle of (a ship or aircraft) • she was lying almost abeam of us
• [as prep.]
before I knew it, I was abeam the ship.
– origin mid 19th cent.: from a-2 (expressing general direction) + beam.