All 6 Uses of

instantaneous
in
Atlas Shrugged

To the rhythm of his body, with the scorching heat on his face and the winter night on his shoulder blades, he was seeing suddenly that this was the simple essence of his universe: the instantaneous refusal to submit to disaster, the irresistible drive to fight it, the triumphant feeling of his own ability to win.†
Chpt 2.3

instantaneous = immediate (happening with no delay)

It was not a progression of words, but the instantaneous verdict of an emotion, a verdict that told him: This, then, was his nature, this was his depravity-that the shameful desire he had never been able to conquer, came to him in response to the only sight of beauty he had found, that it came with a violence he had not known to be possible, and that the only freedom now left to him was to hide it and to despise himself, but never to be rid of it so long as he and this woman were alive.†
Chpt 2.6

She stood looking up at the structure, her consciousness surrendered to a single sight and a single, wordless emotion-but she had always known that an emotion was a sum totaled by an adding machine of the mind, and what she now felt was the instantaneous total of the thoughts she did not have to name, the final sum of a long progression, like a voice telling her by means of a feeling: If she had held onto Ouentin Daniels, with no hope of a chance to use the motor, for the sole sake of knowing that achievement had not died on earth-if, like a weighted diver sinking in an ocean of mediocrity, under the pressure of men with gelatin eyes, rubber voices, spiral-shaped convictions, noncommittal so†
Chpt 3.1

The sudden screech of the microphone jerked the crowd into an instantaneous attentiveness; people seemed to be a second's worth of self-control away from panic.†
Chpt 3.3 *

He was laboring to sound cynical, skeptical, superior and hysterical together, to sound like a man who sneers at the vanity of all human beliefs and thereby demands an instantaneous belief from his listeners.†
Chpt 3.3

It was not the pressure of a hand that made her tremble, but the instantaneous sum of its meaning, the knowledge that it was his hand, that it moved as if her flesh were his possession, that its movement was his signature of acceptance under the whole of that achievement which was herself-it was only a sensation of physical pleasure, but it contained her worship of him, of everything that was his person and his life-from the night of the mass meeting in a factory in Wisconsin, to the Atlantis of a valley hidden in the Rocky Mountains, to the triumphant mockery of the green eyes of the superlative intelligence above a worker's figure at the foot of the tower-it contained her pride in herself†
Chpt 3.5

Definitions:

(1) (instantaneous)
immediate (happening instantly with no delay)
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

In physics, instantaneous can mean at a specific instant (an unmeasurably short time period) -- such as "instantaneous velocity".