CSS: referencing other definitions

I've been looking high and low, and have been unable to find an answer to this. I've heard that in a css you can define a style by referring to another, for instance, you define something like this:

and if you want to then define another element, to be basically the same (for instance, you want it bold) you can refer to this, so if in the future you want to change it slightly (like the color) it is no problem.
Is it also possible to do it with redefining tags--so if you want text in a <td> and a to be the same, it is no problem.
Thanks in advance.

I am guessing you mean something like this:

Not really. Maybe this will be a better example:
As most of the standard text in a page is in a table and/or a paragraph, I may want them to be the same. What I want to do is redefine the and <td> tags. Is there a way to redefine the tag (setting font style, etc), and in the redefinition of the <td> tag can I refer to the tag so the font will be the same (in case I forget to put text in a table inside a tag). This way, if I want to change the font from TimesNewRoman to Verdana, I just have to change the tag.
Thanks.