Definitions of aboard:

• adverb:   on first or second or third base

  Example: "Their second homer with Bob Allison aboard"

• adverb:   on a ship, train, plane or other vehicle
• adverb:   part of a group

  Example: "Bill's been aboard for three years now"

• adverb:   side by side

  Example: "Anchored close aboard another ship"