How do you randomly select a word from a list like below:

dog
cat
mouse
goldfish
pig
cow

and display it in a text box when a button is clicked, but where one word will not appear more than once each time the program is run? So, for example,

1st click: pig
2nd click: mouse
3rd click: dog
4th click: cow
etc. But NOT

1st click: pig
2nd click: dog
3rd click: mouse
4th click: pig

Any ideas?