I am new to RMarkdown, so maybe I'm missing something. But I've looked for most of this afternoon and still have not found a solution. Hopefully you can help. Here's the problem.
I have a R Notebook to which I am trying to add a list of variable descriptions. Here is a crude set of specifications for the list:

Entire list is indented by, say, 1/2 inch.

Variable symbol (name) is the leftmost item. They are left justified and aligned.

Symbols (names) can be Greek characters, subscripted, or superscripted.

Total width of the symbols range from one to nine characters.

Descriptions are indented at least 3 characters to the right of the widest symbol.

Descriptions are also leftjustified and align at the indented horizontal point on the page.
Here is an example of what this might look like (notice I can't leftalign the descriptions):
_A_c_ Area of a circle [A sub c]
_π_ Mathematical constant (= 3.14159 ...)
_r_ Radius of a circle
_r^2_ Value of r squared
g_variable Growth rate of "variable"
Here I've had to use markdown to format the column of variables. Here any internal underscores subscript the following term, and a carat (^) superscripts the following term.