envelopes is a form of:

Acceleration



noun
1.
~ (in something) (increase of speed) ការកើនឡើង
Example: Tan acceleration in the pulse rate of a runner.
Example: The car accelerated as it over took me.
2.
ការបង្កើនល្បឿន
ENGLISH MEANING
noun
1.
The act of accelerating, or the state of being accelerated; increase of motion or action; as, a falling body moves toward the earth with an acceleration of velocity; -- opposed to retardation.
1.
dispatch, expedite, facilitate, forward, hasten, hurry, push, quicken, rush, speed
1.
block, hinder, impede, retard, slow