Aground — Touching the bottom, or stuck on it.
Aids to navigation — Artificial objects that mark safe and unsafe waters.
Amidships — The center of the boat, or toward it.
Anchorage — A suitable place to drop the hook based on wind, sea and bottom conditions.
Astern — In back of the boat (opposite of ahead).
Aweigh — The position of the anchor as it’s raised clear of the bottom, as in “anchors aweigh!”