a scopophiliac, 1889 as a French word in English, from French voyeur, literally "one who views or inspects," from voir "to view," from Latin videre "to see" (from PIE root *weid- "to see").
Je ne puis pourtant omettre une catégorie de sadistes assez étonnants; ce sont ceux qu'on désigne sous le nom de "voyeurs." Ceux-ci cherchent une excitation dans les spectacles impudiques. [Léo Taxil]
-ism
word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.