Sortable isn't a word?

I was writing a description of a program today:

The list is sortable by class, assignment name and due date

And MS Word underlined sortable and suggested:

storable
sort able
portable
suitable
settable

What?!!

A search on dictionary.com revealed no definition for sortable under sort, yet a Google search returned 2,430,000 results for sortable! It's kind of odd to find that a word you assumed was a word, isn't really official. (Note: a search for lol on dictionary.com returned a result.)

We need to sort this out. If not sortable, then what? "can be sorted" seems so....blech.


P.S. A Google search for lol returned 540,000,000 results....but still...