Non-Mailable
Defined in 1 dictionary — Black's (1910)
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
A term applied to nil letters and parcels which are by law excluded from transportation in the United States malis, whether on account of the size of the package, the nature of its contents, its obscene character, or for other reasons. See U. S. v. Nathan (D. C.) 61 Fed. 936.