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                           general:: 
                            Phrase(s): in one’s element 
Fig. in a natural or comfortable situation or environment.  •  Sally is in her element when she’s working with algebra or calculus.  •  Bob loves to work with color and texture. When he’s painting, he’s in his element.
                        
                        
 
                        
                            McGrawhill's American Idioms And Phrasal Verbs