Several news outlets have reported that calling the Russo-Ukrainian War a "war" is illegal in Russia since a law was passed in March 2022.
Putin signed a law that would punish anyone who shares "false information" about the war in Ukraine. [...] Protesters wielding "No to war!" signs in reference to the Russian invasion in Ukraine fall under the new order and could be fined up to 50,000 rubles ($448) [...]
Free speech and reporting may be another casualty of the Russian invasion of Ukraine, and President Putin signed a law making the airing of what the government calls false information about the armed forces illegal. Journalists could be jailed for up to 15 years. Russian officials assert it's false to call their military operations in Ukraine a war or an invasion.
However, some outlets add a qualifier such as "effectively" or "apparently" to their statements, so I'm unsure how unequivocal the law is in that respect.
Putin signed a law in March that effectively made it illegal to call the invasion a war.
I cannot find any cases in which people have been charged with simply using the term "war" in Russia to describe the war.