Dishwater is the dirty, soapy water left in the sink after washing dishes. It's usually gray or cloudy, filled with food particles, grease, and soap suds from scrubbing plates, cups, and silverware.

The word appears most often in the phrase dull as dishwater (sometimes called dull as ditchwater), which describes something incredibly boring. If someone says a movie was as dull as dishwater, they mean it was so tedious they could barely stay awake. A lecture that drones on and on might be described this way, or a book with nothing interesting happening in it.

Why compare boring things to dishwater? Because dishwater just sits there, murky and lifeless, with nothing appealing about it. It's the opposite of sparkling, clear, fresh water. Nobody wants to look at dishwater or think about it any longer than necessary.

You might also hear someone describe weak coffee or tea as tasting like dishwater, meaning it's so watered down it has almost no flavor. The comparison works because dishwater represents something that started out useful (clean water and soap) but ended up as something nobody wants.