Google normally stores the keywords and items you search in Google Play Store. These are similar to Google search suggestions which are shown when you search for any keyword. This can be annoying for users because Google Play Store responds more slowly.
Open Google Play Store and tap on the menu button. Then tap on the Settings button.
Under Settings, search for Clear Search History option under General tab and tap it.
Note that no special icon comes up, it just clears the search history.