noun
overseas traveler; passenger (on an international voyage)
Refers specifically to a person traveling abroad, especially by ship or air. More formal and narrower than 旅行者.
空港には多くの渡航者が集まっていた。
Many overseas travelers gathered at the airport.
渡航者はパスポートを提示する必要がある。
Overseas travelers must present their passports.
乗客 is a passenger on any vehicle (train, bus, plane, etc.), while 渡航者 emphasizes the act of crossing the sea or traveling abroad.
Compound of 渡航 (overseas voyage) + 者 (person).