I'm creating an application for the iPhone where the user has the ability to star an item, i.e. adding a star to the item. Now I am wondering whether I can also use unstar? Or should I go with something different - if so, what?
The verb to unstar is not reported in the dictionary I have, which doesn't report to unpublish either.
If to star refers to an action that changes the status of something, then to unstar would be understood as the action that makes the opposite status change.
This is what happens with to unpublish, which is understood as to change the status to not published.
Unstar is commonly used in applications such as Gmail. I would say yes, it's acceptable to use in the context of software.
i am not sure about unstar but you can definitely use Unstarred as gmail and other e-mail provider use in there action buttons
i think it is obvious that "to unstar" something is to set a value to 0 that was once a 1, with a star icon displayed, but if you read the linked question there seems to be a bit of confusion in the general public as to how "to star" should be interpreted as a verb.
basically, "star" is not a verb, so neither is "unstar" but if you do decide to use one as a verb you might as well use the other to be consistent.
you'd be safer using actual verbs from the dictionary, saying "remove a star" alongside a clear concept of what "adding a star" means.
Is it really difficult to say "remove a star", which all readers will understand instantly, without needing to refer to a glossary?
Whether or not this activity requires the inclusion of a new word in the English language remains to be seen, but it isn't there yet, so why make life difficult for yourself? Fretting over it has probably taken up much more of your time and energy than typing the extra few characters would have.
Just use words that say what you mean, and will be understood by your readers -- i.e. in this case, if you're writing for GMail users, go ahead and use "unstar"; if you're not, consider using real words.