Part of speech: Adverb
on a ship, train, plane or other vehicle
Part of speech: Adverb
on first or second or third base
Example: Their second homer with Bob Allison aboard
Part of speech: Adverb
side by side
Example: anchored close aboard another ship
Part of speech: Adverb
part of a group
Example: Bill's been aboard for three years now
On board, On base, Alongside, Aboard
The word "aboard" comes from Middle English abord.
– A related word in the same word family.
board – A related word in the same word family.
Many Middle English words had multiple spellings because standardization didn't exist yet.