Caroline Jarrett’s 2 rules for labeling buttons (found via elearning post):

• Label the button with what it does
• If the user doesn’t want to do it, don’t have a button for it

“The consequence of the two rules may be that you end up with buttons with labels that are longer than a single word. I think that’s much better than striving for single words that are either confusing … or infuriating ….”