Quote Originally Posted by doninphxaz

It's very common for us to say, "Go look it up in the dictionary." The assumption is that the person has a dictionary and that they have only one, thus "the" works in that context.

"Go look it up in a dictionary" is fine as well.
I think we say the dictionary in the same way we say the bible. As there was only one when they both begun. But these days there are many forms of dictionarys and bibles, so it would probably be more accurate to say a dictionary or a bible.
But old habits die hard and I dont doubt Ill still say "Ill have a look in the dictionary" even though I have several.