English word aboard comes from Middle English (1100-1500) a-, Middle English (1100-1500) bord

Detailed word origin of aboard

Dictionary entry	Language	Definition
a-	Middle English (1100-1500) (enm)
bord	Middle English (1100-1500) (enm)
abord	Middle English (1100-1500) (enm)	(nautical) Alongside.. On board; into or within a ship or boat On board of; onto or into a ship, boat, train, plane.
aboard	English (eng)	(baseball) On base. [First attested in the mid 20th century.]. (nautical) Alongside. [First attested from around (1350 to 1470).]. Into a team, group, or company. [First attested in the mid 20th century.]. On board; into or within a ship or boat; hence, into or within a railway car. [First attested from around (1350 to 1470).]. On or onto a horse, a camel, etc. [First attested in the late [...]

Words with the same origin as aboard