The term "atomic cannon" specifically refers to a type of artillery piece that can fire projectiles with nuclear warheads. If we consider synonyms for this term, some possible options could include similar types of artillery, such as a howitzer or a mortar. However, these terms do not necessarily convey the concept of nuclear power. Other related terms might include "nuclear artillery" or "atomic artillery," which could refer to a broader range of weapons. Overall, synonyms for "atomic cannon" would depend on the context and the specific meaning that is intended, and may include more general terms like "military weaponry" or "nuclear arms".