modified
Rapid
Almost immediate
Hasty
Alert
quick, in this comparison, implies ability to respond rapidly as an innate rather than a developed faculty a quick mind; prompt stresses immediate response to a demand as resulting from discipline, practice, etc. or from willingness prompt to obey, a prompt acceptance; ready also implies preparation or willingness and, in another sense, connotes fluency, expertness, etc. a ready sympathy, ready wit; apt, in this connection, implies superior intelligence or a special talent as the reason for quickness of response an apt pupil
See quick in Webster's New World Roget's A-Z Thesaurus II
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