Verisimilitude means being believable, or having the appearance of being true. You can improve your play by using the sounds and smells of the beach as well as lots of sand to create verisimilitude.
Verisimilitude comes from the Latin verisimilitudo "likeness to truth" and is used to describe stories. In it, you'll see the word similar, meaning it is similar to what's real. Art that aims for realism seeks verisimilitude. An actual synonym for verisimilitude is truthlikeness. Tell that to your friends, and they'll probably think that your story lacks verisimilitude.