A list of prohibited items for carry on luggage can be found at TSA.gov under the Traveller Information tab on the Prohibited Items page. In addition to an extensive, detailed list, there is also a search option available for specific items not covered.
Items listed on the Prohibited Items page are accompanied by instructions on how to handle the items that are being transported, for example, firearm and ammunition. Additionally, the TSA lists what items may be carried in checked luggage when not allowed in carry-on luggage. Even though an item may be listed as allowed, if it sets off alarms during security it may be confiscated. It is important to check this list frequently, as it is constantly changing.