The history of the word passenger, meaning “someone on some sort of conveyance,” is a bit surprising. In the 1300s, a passager was the pilot of a ferry, not one of the other people on board. Later passager acquired what linguists call an intrusive N or parasitic N, and came to apply instead to the people being transported. A similar phonetic process gave us the words messenger, which was originally messager, and scavenger, originally scavager.
This is part of a complete episode.