Based on few comments words (querystring, gridview, etc), I assume you are working on a web application and it's an ASP.NET app code.
If so, you need to bind the items once defined to the list.
Post fetching the values, do:
oleda.SelectCommand = cmd;
oleda.Fill(dt);
lstInstalledWord.Items.Clear();
lstInstalledWord.DataSource = dt;
lstInstalledWord.DisplayMember = "words";
lstInstalledWord.ValueMember = "words";
lstInstalledWord.DataBind();
Once you define the datasource, you need to bind too. Try!