How Did April Get Its Name?
All months of the Gregorian calendar used today have their roots in the ancient Roman calendar, and many of those months have pretty boring names — September through December are literally just named for numbers, according to Almanac. Two months are named for historical people (Caesars Julius and Augustus get the seventh and eighth months) and four months are named for classical gods or goddesses, leaving two months with names that are somewhat unusual — February, which may have been named for an early Roman spring festival, and April.
April is thought to come from the Latin word "aperire," meaning "to open" (this is also the root of "aperture," "aperitif," and even "overture," according to Merriam-Webster). This might refer to the opening of flowers from buds, according to the British Museum. An alternate and less widely accepted explanation for the name is that it comes from Aphrodite, the Greek goddess that became the Roman goddess Venus; Romans celebrated Venus's festival on the first day of April, according to WordInfo.
April in Ancient Rome
Though April always came in spring, it was originally the second month of the Roman calendar, not the fourth — the period that is now January and February was originally a mass of 61 unassigned winter days (per Rome on Rome). This is why December comes from the Latin root for ten and not twelve.
April in Ancient Rome — called Aprilis — was apparently a bustling time. By the time the Julian calendar was implemented (via the University of Chicago), Aprilis had 30 days (as April does now) and several springtime festivals. In addition to Venus' festival, Romans celebrated the Vinalia Priora, to bless the wine casked the previous autumn, on April 23; Robigalia, when dogs were sacrificed to keep the harvest free of disease, on April 25; and Floralia, a bawdy flower festival, on April 28. Perhaps most importantly, on April 21 Romans celebrated Parilia, which was both another agricultural festival and a celebration of the founding of Rome (per Britannica).