unlight

From un- +‎ light; or perhaps from Middle English *unlighten (suggested by past participle unlight, unlyght, unliȝt (“unlit”)), equivalent to un- +‎ light.

unlight (third-person singular simple present unlights, present participle unlighting, simple past and past participle unlighted or unlit)

1. (transitive, rare) To extinguish, turn off, or dim the light from
   • 2002, Ilya Kaminsky, Ilya Kaminsky Greatest Hits:

     His father, in another room, unlights the lamp and leaves the world alone.

   • 2005, ‎Conrad H. Gempf, Mealtime Habits of the Messiah:

     Remember Obi-Wan Kenobi in the first Star Wars film? At one point in the big duel, he unlights his light sabre and stands defenseless but confident before Darth Vader, saying sonorously, “If you strike me down, I shall become more powerful than you can possibly imagine.”

From Middle English unlighten (“to lighten the burden of; alleviate; dismount from horseback”), equivalent to un- +‎ light (“to alight”).

unlight (third-person singular simple present unlights, present participle unlighting, simple past and past participle unlighted)

1. (intransitive, now dialectal) To alight; dismount
   • 1838, Edward Lanzer Joseph, Warner Arundell the adventures of a creole:

     I would rather take the water unmixed," said I. "Just as you like," said the old soldier; "but please to unlight, and come into my barracks, at all events."

   • 2015, Bertrand Harris Bronson, The Traditional Tunes of the Child Ballads:

     Unlight, unlight, you gay Lady Unlight of your middle quite speed Deliver it unto me For I seems it looks too rich and too gay To melder all in the salt sea.