The only two-letter word containing the letter Z; invented by Scrabble players in order to capitalize on that letter's high point-value.
A: Ha! Look at my bingo: ZODIACS! Since the Z is on the double-letter box and the A is on the triple-word box, I get 87 points for the word, plus a fifty-point bonus for using all my tiles, giving me a total of 137 points for this turn.
B: Pshaw! I could've done it too. You just got lucky.
A: Wait a minute! I also get an additional 21 points for ZA, which raises the grand total to 158 points!
B: Egad! If I had any say in the matter, "ZA" never would have been admitted into the Scrabble dictionary! Who the heck actually uses the word?