Why is it called "escape velocity" and not "escape acceleration"? As we know, velocity to escape from an orbit is in proportional with the orbital velocity:
$$v_\mathrm{escape}=\sqrt{2}v_\mathrm{orbit}$$
Since, orbital velocity decreases as we move away so should be velocity to escape from it. In other words farther is an orbit lesser will be velocity to escape from it.
Thus, as we move away the value of velocity with which we need to escape decreases. Now isn't that actually negative acceleration? We need to have that acceleration in order to escape. 
Why then we call it as escape velocity instead of escape acceleration?
(And, if I am correct is it just opposite of gravitational acceleration?)
 A: I think the issue is a lot clearer if you think in terms of energy. When you're on the surface of the Earth, you're in a gravitational potential well. You need a certain amount of kinetic energy to "climb out" of the potential well, and since velocity is a visible (and less abstract) proxy for kinetic energy, it's common to speak of escape velocity.
A: I think this is just down to a minor misunderstanding of terminology.
If I place a rock, say, near the Earth, with a velocity high enough to escape the Earth's gravity. It will only have acceleration based on gravity; as it is unpowered, but whether or not it escapes will depend entirely on whether its velocity is above the escape velocity for the position it is in. 
That velocity will change, and Earth's gravity will continue to slow the rock as it heads away from the Earth. But the rock isn't going to be able to accelerate against gravity - it's a rock. It can still escape though...
Yes, the velocity required will reduce in proportion with the orbital velocity, but that in no way defines an escape acceleration. 
A: Escape acceleration is the right idea.
Let’s look at the dimensions of acceleration.
A= Length/Time^2
You do have to have greater acceleration that gravity, but if you’ve ever jumped rope or jumped up for a rebound, you know you’ve had escape acceleration. The trick is to do it for long enough.
Hence:
Length/Time^2    Mulitplied by Time gives you
V=Length/Time, a velocity... an escape velocity. This also explains why escape velocity is less the higher orbit you are and how it is a function, ultimately, of the gravity well caused by the mass of the body.
