Definition of quantum noun from the Oxford Advanced Learner's Dictionary

 

quantum

 noun
noun
BrE BrE//ˈkwɒntəm//
 
; NAmE NAmE//ˈkwɑːntəm//
 
(pl. quanta
BrE BrE//ˈkwɒntə//
 
; NAmE NAmE//ˈkwɑːntə//
 
)
(physics)
 
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a very small quantity of electromagnetic energy Word Origin mid 16th cent. (in the general sense ‘quantity’): from Latin, neuter of quantus ‘how great, how much’. The current sense dates from the early 20th cent.
See the Oxford Advanced American Dictionary entry: quantum