my word!

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(upon) my word

An interjection expressing surprise, amazement, or incredulity. Upon my word, I cannot believe that my own wife would stoop to such depths of treachery! My word, Jenkins, this report is simply terrible. You're going to have to do better than that if you want to stay in this company.
See also: word
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

(upon) my ˈword!

(old-fashioned) used to express surprise: My word! That was quick!
Farlex Partner Idioms Dictionary © Farlex 2017
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References in classic literature ?
My word! His blood'd breed true for a thousand generations, and the cool head and the kindly brave heart of him."