Possible Clues:

• End-of-the-workweek exclamation
• Working for the weekend letters
• "Yay! No work tomorrow!"
• 9-to-5er's cry
• Worker’s shout
• Weary worker's letters
• Abbreviation said with a 'Whew!'
• "It's been a WEEK!"
• Weekend lover's abbr.
• "The weekend is almost here!"