Akademik

a viewer who enjoys seeing the sex acts or sex organs of others

noun, pl ⋯ Toms [count]

: a person who secretly looks into other people's windows to see them naked

ˌPeeping ˈTom noun (disapproving)

a person who likes to watch people secretly when they are taking off their clothes

Syn: ↑voyeur

[Peeping Tom] from the name of the person said to have watched Lady Godiva ride naked through Coventry.  

The phrase ‘Peeping Tom’ comes from the story of Lady Godiva, who rode through the streets naked. Everyone was told not to look at her, but one man, ‘Peeping Tom of Coventry’, did and he went blind

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He realized that he was watching the lovers like a common Peeping Tom.