formatting - One-column table not properly displayed by TableForm

I want a table with a single column of data, and with headings along both the rows and the column. One might expect it to work like this:

TableForm[{"one", "two", "three"}, 
 TableHeadings -> {{"$10MM", "$20MM", "$30MM"}, {"col"}}]

But this does not work; it displays the data and the row labels correctly, but it does not label the column. What am I missing?

Answer

You present a single row vector to TableForm, which is rather hankering for a column vector (or matrix).

Instead of {"one", "two", "three"} you need {{"one"}, {"two"}, {"three"}}. There are many ways to achieve this, one of them List /@ {"one", "two", "three"}:

TableForm[List /@ {"one", "two", "three"}, 
 TableHeadings -> {{"$10MM", "$20MM", "$30MM"}, {"col"}}]