Wow!

Wow, first seen in Scottish in the 1510s, is a natural expression of amazement. When you are amazed, your mouth drops open and almost automatically makes a ‘wow’ sound as you exhale.  The word was very popular in the early 1900s and again in the 1960s (Online Etymological Dictionary).
 
The noun ‘wow’ (an unqualified success) is from 1920. The verb ‘to wow’ (to overwhelm with delight or amazement) is from 1924.
 
Reference: Online Etymological Dictionary, https://www.etymonline.com/
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