The SCOWL is a collection of word lists organized by word popularity, language, word class, and other factors. These lists can be combined in various ways (or used individually) for spell checking and similar purposes.
The Debian wamerican*, wbritish*, and wcanadian* wordlist packages are built from (appropriate collections of) these same lists. Install one (or more) of those packages if you want a comprehensive word list; install scowl if you (also) want to pick and choose the pieces that comprise those lists.
You can learn more about SCOWL (and other English word lists) at http://wordlist.sourceforge.net/