1. [adv]  (baseball) on first or second or third base; "Their second homer with Bob Allison aboard"
2. [adv]  on a ship, train, plane or other vehicle
3. [adv]  part of a group; "Bill's been aboard for three years now"
4. [adv]  side by side; "anchored close aboard another ship"

ABOARD is a 6 letter word that starts with A.

1. \A*board"\, adv. [Pref. a- on, in + board.]
   On board; into or within a ship or boat; hence, into or
   within a railway car.
   2. Alongside; as, close aboard. Naut.:
   {To fall aboard of}, to strike a ship's side; to fall foul
      of.
   {To haul the tacks aboard}, to set the courses.
   {To keep the land aboard}, to hug the shore.
   {To lay (a ship) aboard}, to place one's own ship close
      alongside of (a ship) for fighting.
   

2. \A*board"\, prep.
   1. On board of; as, to go aboard a ship.
   2. Across; athwart. [Obs.]
            Nor iron bands aboard The Pontic Sea by their huge
            navy cast.                            --Spenser.