#!/bin/bash
echo -n "Please enter a word pattern to search for (use a . for unknowns): "
read text
echo `grep -w $text /usr/share/dict/words`
Just paste into your text editor of choice, save somewhere, make sure to chmod +x the file and boom, you have yourself a very simple crossword solver! Granted it isn't perfect, but it's a good start.
[robg adds: Just to clarify, the Unix dictionary isn't the same as the built-in dictionary you access through the Dictionary program. While the Unix words file does hold a large number of words, it doesn't have everything you'll find in Dictionary app.]

