how do i make a thin glaze instead of frosting, for a bundt cake?

Just add a little milk to the sugar until you reach the consistency you want. You can flavor it how you like, such as a teaspoon of vanilla extract to 4 cups of confectioners sugar, or make a different flavor like peppermint extract or almond extract (I don't have my recipes in front of me, so start with very small amounts of extract so you don't ruin it - you can always add more flavoring). I think I've used espresso powder to make coffee flavored, too. Lemon or orange juice work great too. Anyway, for most recipes you just add milk or cream till it's the right consistency. Easy peasy :)

I just dump a bunch of confectioners' sugar in a bowl and add enough liquid until I have the consistency that I want. If it gets too thin, I add more sugar.

I've liked & used this one for years (from Bertolli olive oil company). mix 1.5 cups confectioners sugar, 3 tbsp lemon juice, 1 tsp lemon zest, 1 tbsp extra virgin olive oil.
or this one from epicurious, if you want vanilla but not lemon notes:
http://www.epicurious.com/recipes/food/views/basic-sugar-glaze-51157020
(more or less same ration of liquid to sugar)
enjoy!