An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Occurring, done, or completed in an instant.
2) Existing at or pertaining to a particular instant (Dictionary.com).

→ instant; → -an; → -eous.

The → acceleration of a particle at time t defined by a = lim Δv/Δt = dv/dt. It is the limiting value of Δv/Δt at time t as both Δv and Δt approach zero.

→ instantaneous; → acceleration.

The velocity of a particle at some one instant of time, or at some one point of its path. It can be defined as the limiting value of the average velocity when the second point is taken closer and closer to the first point.

→ instantaneous; → velocity.