An airmail envelope with a distinct pattern of spaced diamonds in alternating red and blue colours around the outer edge.

plural of Dahlke envelope

(marketing) A plain envelope with no window showing the contents, used to make junk mail resemble legitimate correspondence.

plural of blind envelope

Synonym of hongbao

Alternative form of back-of-the-envelope

plural of nuclear envelope

(biology) nuclear membrane

(rail transport) The outline of the space occupied by a rail vehicle when in motion, including the effects of tilt, sway, track cant, etc.

(US) An envelope whose mailing for an authorized purpose does not requiring postage, while its unauthorized use may be penalized.