(slang, US) April 15, tax day in the United States
2017, "Alastair Paterson ", Beware the Ides of April - Cybercriminals and Tax Season (in Security Week)
Although the consequences aren’t as dire, a similar warning is also in order for businesses and individuals in the U.S. around the Ides of April – the traditional tax filing deadline and, in recent years, a deadline for cybercriminals to profit from tax season.
2020, "Lawrence A. Zelenak", A Very Special Tax Episode (in Forbes)
There's a an episode from The Odd Couple in 1973 called, "The Ides of April," where initially Felix gets audited.
