Dream dictionaries are bull

And, talking about bulls, if I did dream about a bull, it would mean something to me that's quite different from what it might mean to a dairy farmer in Wisconsin, a Hindu in India, a matador in Spain or someone who had never seen a bull. 

Dream images do have powerful meanings that are largely independent of our own interpretations. A bull is for many westerners a symbol of masculinity and power. But even then, masculinity can have different meanings. If you are a woman and dream about a bull, what does that signify? And more, masculinity might mean a man's ability to fight, to argue or his abilities as a lover of women. Masculinity is not one thing, neither is power. 

For most Americans, the bull  is so distant from our everyday lives that it really is more of a symbol; If your wealth depended on the family bull, it'd mean something very specific and real to you.

Perhaps a dream dictionary would work in a society that was very small and uniform (but I doubt it). In our complex society, dreams images depend on what meaning you give to them.

For example:

If I dream about San Francisco (I go there every week), it'll have a completely different meaning for me than if someone in Moscow or Cairo or Beijing dreams about going to San Francisco.

When Jung analyzed a dream in which he was in Liverpool, it indicated the "Pool of Life" to him. When I dream about Liverpool  (I used to live on High Park Street in L'pool 8), it refers to a very specific (and wild) period of my life.

The dream dictionary at it's best is almost OK

At best they are like buses: they get you from near where you are to near where you want to be.

A Common Dream Symbol: Teeth falling out

Let's take one of the most common dreams: Your teeth falling out.

Rather than have a blanket answer for all the billion human beings on this planet, 
consider these questions:

These answers will help you to ground the dream in your own meaning. Of course there is something universal about teeth falling out -- it happens everywhere -- but that is only a piece of the jig-saw puzzle about what it meant in your dream. Consider the fact that a US $5 bill is the same every where in the world but what you can buy with it will be quite different in Manchester, Mozambique and Manhattan.

Build your own dream dictionary

Here's a better way of developing an understanding of the symbols in your dreams.

If you have a dream diary and can look over a number of dreams (say 50 or more), you can build up your own dream dictionary. 

You'll find that some images and themes crop up over and over. 

You'll also find that some of them develop as time goes by; So, remember to update you dictionary, it will change faster than Webster's.