how, what, why, etc. on earth...

how, what, why, etc. on ˈearth...

,

how, why, etc. in the ˈworld...

(informal) used with questions to express the speaker’s surprise, anger, etc: How on earth did you know I was coming today when I didn’t know myself until the last minute?Why on earth would anyone give up such a good job?
See also: on