Webster's Revised Unabridged Dictionary · 1913

Black letter

Black letter ({not transcribed})

The old English or Gothic letter, in which the Early English manuscripts were written, and the first English books were printed. It was conspicuous for its blackness. See Type.

Black-letter , adjective

1.
Written or printed in black letter; as, a black-letter manuscript or book.
2.
Given to the study of books in black letter; that is, of old books; out of date.
Kemble, a black-letter man! — J. Boaden
3.
Of or pertaining to the days in the calendar not marked with red letters as saints' days; -- compare red-letter.
Unlucky; inauspicious.