English
lightproof
From light + -proof.
A compound of light + -proof
Proto-Indo-European *lewk- ‘to shine’
…
Proto-Germanic *leuhtą
Proto-West Germanic *leuht ‘light’
Old English lēoht
Middle English light ‘light, illumination’
English light
Today it means
adj Sealed so that no light can enter.
Language periods are conventional ranges, not dates for this word.
Etymograph / lightproof