Why is Autumn the only season with two names?
It's interesting: Before it was autumn and fall, it was harvest.
While the modern names of winter and summer have been around for more than 1,000 years, the names of fall and spring are more recent—and less constant. This is partly because the two seasons were long viewed as secondary to summer and winter.
As late as the 18th century, English speakers were less likely to think of the year as having four seasons, focusing instead on the coldest and warmest portions of the year.