There are already nuclear armed “terrorist nations”. Notwithstanding that “terrorist” is subjective and loaded term.
There aren’t any nuclear-armed nations that have not, while being nuclear powers, been either practitioners of internal state terrorism (the original sense of “terrorist”) and/or sponsors of such regimes and/or of non-state terrorists working against their geopolitical rivals.
Russia, as a nuclear state, has armed the Wagner Group, which France, a nuclear state, has described as terrorist.
Israel, a nuclear state, has armed settlers in the West Bank, which can be described as terrorists.
Israel, a nuclear state, has engaged and participated in terrorist activities in the past. Israel probably got their first bomb in 1963, Israel was using car bombs against PLO officials as late as 1981 via terrorist fronts.
You're going to have to come up with an incredibly convoluted definition of terrorism in order to have it include only people, groups or countries you dislike, but not include people, groups and countries that you do like. And if you do that, then it goes back to the comment by the person you replied to that said that "terrorist" is a subjective term. If you apply consistent rules and definitions, then most governments in the world will be found to be conducting terrorist activities, and mutual accusations of it lose any meaning.
(and no, israel and the US never aimed at civilians. They've used armies to fight armies.. which doesn't mean there hasn't been civilians casualties of course).
The hijacking of American Airlines Flight 77 which targeted and hit the Pentagon—a military target—was a terrorist attack, albeit with heavy civilian casualties. The suicide bombing of USS Cole by al-Qaeda in October 2000 is considered a terrorist attack. It is hard to find less civilian target then a military attack missile destroyer.
The atomic bombings of Hiroshima and Nagasaki in August 1945 are not considered terrorist attacks despite the targets being civilians and the goal being political (unconditional surrender and a regime change of imperial Japan).
Wikipedia describes terrorism as “the use of intentional violence and fear to achieve political or ideological aims.” Wikipedia also warns this is a very broad definition, hinting that it is not that simple. Later in the article Wikipedia admits: “The definition of terrorism lacks universal agreement” This is in contrast to e.g. Genocide, which Wikipedia offers a precise criteria outlined by the UN Genocide convention. The truth is there is nothing simple about what is and isn’t terrorism. It varies by who is using the term and in what context. It is one of these Wittgensteinian prototypical terms which only gets defined via its use.