(noun) "someone who travels in, but does not operate, a vehicle"
The modern sense was developing in English during the 16th century: a boat or a coach could have passengers. But the older sense, which arrived in the language in the early 14th century from French, had nothing to do with vehicles. A passenger was simply a wayfarer, a traveller, a passer-by. This is how Shakespeare uses the word, and usually in dangerous contexts. The only instance of a non-threatening sense is in Venus and Adonis (line 91), when the poet describes Venus's desire for a kiss: "Never did passenger in summer's heat More thirst for drink than she for this good turn". In the other six instances where the word appears, passengers are being robbed, fleeced, chased, suffering outrages, or even (as the Queen remarks in Henry VI Part 2, III.i.227) being eaten: "Gloucester's show (i.e.
appearance)Beguiles him as the mournful crocodile With sorrow snares relenting passengers". When the First Outlaw says to the others (in Two Gentlemen of Verona, IV.i.1), "I see a passenger", we know a robbery is afoot.