the outer boundary of an artifact or a material layer constituting or resembling such a boundary | the apparent surface of the imaginary sphere on which celestial bodies appear to be projected |
a device that provides reactive force when in motion relative to the surrounding air; can lift or control a plane in flight | |
a superficial aspect as opposed to the real nature of something | |
information that has become public | |
the extended two-dimensional outer boundary of a three-dimensional object | |
the outermost level of the land or sea | |