[ 'ɛnvələʊp , 'ɒn- ]
■ noun
1》 a flat paper container with a sealable flap, used to enclose a letter or document.
2》 a covering or containing structure or layer.
3》 Electronics a curve joining the successive peaks of a modulated wave.
4》 Mathematics a curve or surface tangent to each of a family of curves or surfaces.
Phrases
push the ( edge of the ) ~ informal approach or extend the limits of what is possible. [orig. aviation sl., relating to graphs of aerodynamic performance.]
Origin
C16 (in the sense 'enveloping layer'): from Fr. enveloppe , from envelopper 'envelop'.