To make gloomy or dark; to cover with gloom or shadow.
From en- (to put into a state) + gloom (origin uncertain, possibly from Old Norse glaumr or related to glow; meaning 'darkness' emerged in 16th century). The en- prefix creates verbs expressing causation or covering.
Gloom itself is a relatively recent English word—it wasn't common until the 1500s—so 'engloom' is even more obscure. The Romantic poets loved coining words with 'en-' to express emotional states: 'enkindle,' 'enliven,' 'encompass the soul.'
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