from
The Collaborative International Dictionary of English v.0.48
Black-letter \Black"-let`ter\, a.
1. Written or printed in black letter; as, a black-letter
manuscript or book.
[1913 Webster]
2. Given to the study of books in black letter; that is, of
old books; out of date.
[1913 Webster]
Kemble, a black-letter man! --J. Boaden.
[1913 Webster]
3. Of or pertaining to the days in the calendar not marked
with red letters as saints' days; -- compare {red-letter}.
Hence: Unlucky; inauspicious.
[1913 Webster]