voyeur

Voyeur is a fairly recent addition to English; our earliest written evidence for the word dates from the beginning of the 20th century. It comes directly from a French noun meaning, literally, “one who sees.”

Initially, voyeur referred to someone who derived sexual pleasure from watching others undress or engage in intimate acts; it was synonymous with PeepingTom. By the middle of the 20th century, its meaning had broadened to "an unduly prying observer," particularly one interested in squalid or shocking details:

[A] good biographer is always in some sense a voyeur.–Times Literary Supplement, November 5, 1971

Is a press that pries into a presidential aspirant’s personal habits pandering to voyeurs or enlightening rightfully curious voters? –Saturday Review, February 16, 1980