Bastardly vs Bastardy - What's the difference?

As an adjective bastardly

is being born out of marriage.

(legal) the condition of being illegitimate, of being born to an unmarried woman or as the fruit of adultery.

(en adjective)

Being born out of marriage.

Of no use or purpose; useless; worthless.

* See also

(legal) The condition of being illegitimate, of being born to an unmarried woman or as the fruit of adultery.

* Shakespeare, Richard III , .

Go, after, after, cousin Buckingham.

The Mayor towards Guildhall hies him in all post:—

There, at your meet'st advantage of the time,

Infer the bastardy of Edward's children:

Tell them how Edward put to death a citizen,

Only for saying he would make his son

Heir to the crown;—meaning, indeed, his house,

Which, by the sign thereof, was termed so.

* bastardy bond