Princeton's WordNet

1. coal black, ebony, jet black, pitch black, sable, soot black(adj)

   a very dark black

2. coal-black, jet, jet-black, pitchy, sooty(adj)

   of the blackest black; similar to the color of jet or coal

Wiktionary

1. jet-black(Noun)

   coal-black; the blackest black

2. jet-black(Adjective)

   coal-black; of the blackest black

Webster Dictionary

1. Jet-black(adj)

   black as jet; deep black

• gitswart, pikswartAfrikaans
• سَبَج، شديد السَّوادArabic
• катранено черенBulgarian
• preto-azevichePortuguese (BR)
• černý jako uhelCzech
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• pigimustEstonian
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• juodas kaip smalaLithuanian
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• ดำสนิท; ดำปี๋Thai
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• 烏黑的Chinese (Trad.)
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• 乌黑发亮的Chinese (Simp.)