You can use $rand(A,Z) and $rand(a,z) to return a random letter from the english alphabet.
If you want to use a word, the easiest way is to do it the way you did it though. Populate a list of words in a variable, separated by $chr(32) which is a space, not null.
http://www.asciitable.com/And then just pull a random number based between 1 and the $numtok of the string.
