Black's Law Dictionary, Sixth Edition, p. 692

Good.  Valid;  sufficient in law; effectual; unobjectionable; sound; responsible; solvent; able to pay an amount specified. 

Of a value corresponding with its terms; collectible.  A note is said to be "good" when the payment of it at maturity may be relied on.

[Black's Law Dictionary, Sixth Edition, p. 692]