Altogether means completely or entirely. When something is altogether different, it's totally different in every way. If your teacher says the class performance was altogether wonderful, she means it was wonderful in every respect, from start to finish.

The word can also mean taking everything into account or considering everything together. If you're calculating how much money you need for a field trip, you might add up lunch, admission, and transportation costs, then say, “Altogether, I'll need twenty dollars.” When a coach reviews the season, she might say, “Altogether, we won fifteen games,” meaning that's the total when you count them all up.

People sometimes confuse altogether with all together, but they mean different things. All together means everyone or everything in the same place at the same time: “Let's sing all together now!” But altogether means completely or in total: “That's an altogether ridiculous idea” or “Altogether, five people came to practice.”

Here's an easy way to remember: if you can split the phrase and insert other words (like “all of us together” or “all grouped together”), use two words. If you mean “completely” or “in total,” use one word: altogether.