Definition of Jekyll and Hyde noun from the Oxford Advanced Learner's Dictionary

 

Jekyll and Hyde

 noun
noun
BrE BrE//ˌdʒekl ən ˈhaɪd//
 
; NAmE NAmE//ˌdʒekl ən ˈhaɪd//
 
[singular]
 
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a person who is sometimes very pleasant (Jekyll) and sometimes very unpleasant (Hyde) or who leads two very separate lives He leads an almost Jekyll and Hyde existence—by day he’s an accountant, by night he’s a singer in a rock band. More Like This Expressions from literary sources Alice in Wonderland, Casanova, Cassandra, Don Juan, Dorian Gray, Falstaffian, Frankenstein, Jekyll and Hyde, Lilliputian, Lothario, Orwellian, Pandora’s box, Peter Pan, Pied Piper, Pollyanna, Rip Van Winkle, Ruritanian, Scrooge, Shangri-La, Sherlock, Stepford Wife, Svengali, Tweedledum and Tweedledee, Utopia, Walter MittySee worksheet. From the story by Robert Louis Stevenson, Dr Jekyll and Mr Hyde, in which Dr Jekyll takes a drug which separates the good and bad sides of his personality into two characters. All the negative aspects go into the character of Mr Hyde.
See the Oxford Advanced American Dictionary entry: Jekyll and Hyde