Definition from Wiktionary, the free dictionary
Probably from a dialectal variant of blee (“complexion, aspect, colour, hue”).
bly (plural blies)
- (now chiefly dialectal) Likeness; resemblance; look aspect; species; character.
- I see a bly of your father about you.
Related terms 
bly n (uncountable)
- lead (chemical element)
Declension of bly