byock means A male ostrich's black and white wing feather.
Etymology
Unknown; the Italian bajocco (“brown”) entered English in the 16th century as byock or baiock (“a small Italian copper coin”), but any relationship with this word seems unlikely.
noun
- A male ostrich's black and white wing feather.“A noticeable feature of the sales was the quantity of fine goods, principally of white and feminas. The best white qualities and good broken brought 10 per cent. to 15 per cent. advance, while other qualities sold firmly. White and light femina were also 10 to 15 per cent. dearer, principally for the best lines. Dark femina and byocks were 10 per cent. higher.”