Quick, prompt, ready, apt are comparable when they apply to persons, their mental operations, their acts, and their words and mean having or manifesting the ability to respond without delay or hesitation.
Quick stresses instancy of response to such an extent that it usually connotes native rather than acquired power. Very often the word suggests marked capacity for learning or for absorbing what is taught.
Prompt also implies instancy of response, but it may or may not imply native quickness. Often it carries a suggestion of preparation (as by training or discipline) that fits one for quick response when the occasion demands it.
Sometimes the word carries so strong an implication of willingness or eagerness that a lack of normal inhibitions is also suggested.
Ready, like prompt, implies previous training or a strong predisposition as well as instancy of response, but it more often characterizes the person or his powers than his performance or his expression of thought or feeling. It therefore often implies, as prompt does not, skill, facility, fluency, or ease in attainment.
The word is often applied to the bodily organ or to the instrument one uses in manifesting skill or fluency.
Apt (see also FIT ) ( APT 2 ) does not throw the emphasis on the quickness of the response, though that is involved in its meaning, but on the possession of qualities (as a high degree of intelligence, a particular talent or gift, or a strong bent) which make for such quickness. It is therefore especially appropriate when the person in mind responds quickly only to particular stimuli or shows a capacity for a definite kind of work.