Definition from Wiktionary, the free dictionary
- Expression of humorous surprise or emphasis.
- You've been divorced four times? Yow!
- Expression of pain; ouch.
- Yow! I dropped it on my toe!
Middle English 
Alternative forms 
From Old English ēow.
- English: you
Unverified; most likely from Old English ēow.
yow personal, emphatic
- (South Scots) you