words selected randomly

Hi
I want to create a simple test in which the visitors are asked to write the meaning of any word selected randomly by a simple java script program"
--each time I refresh my page let my script choose a new "word" out of 20 English words..just like randomly selected numbers(1-20)
can you help me with this?
thanks

var text_st = new Array("String1", "String2", "String3",
"String4", "String5", "String6", "String7", "String8",
"String9", "String10");

var l = text_st.length;

var rnd_no = Math.round((l-1)*Math.random());

document.write(text_st[rnd_no]);