passenger

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A person who travels in a conveyance, such as a car or train, without participating in its operation.
• noun Informal A person who participates only passively in an activity.
• noun A wayfarer or traveler.

from The Century Dictionary.

• noun One who passes or is on his way; a passer-by; a wayfarer; a traveler.
• noun One who travels in a public conveyance; especially, one who travels in such a conveyance by virtue of a contract express or implied with the carrier, as the payment of fare, or something accepted as an equivalent therefor.
• noun A bird of passage; a casual visitor.
• noun A passage-boat.
• noun In a boat-race, one of the crew who adds to the weight of the boat without doing his share of the work; hence, an ineffective member of a football-team, etc.

from the GNU version of the Collaborative International Dictionary of English.

• noun A passer or passer-by; a wayfarer.
• noun A traveler by some established conveyance, as a coach, steamboat, railroad train, etc.
• noun (Zoöl.) a migratory hawk.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One who rides or travels in a train, motor vehicle, boat, ship, ferry, hovercraft, aircraft, etc., but who does not operate it and is not a member of the crew.
• noun falconry A young hunting bird that can fly and is taken while it is still in its first year.
• verb intransitive To ride as a passenger in a vehicle.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a traveler riding in a vehicle (a boat or bus or car or plane or train etc) who is not operating it