Hustle has been an English word since the late 1600s. From Dutch, hustle originally meant “to shake,” but evolved over the years, including “push roughly,” “move quickly,” and “give one’s full effort,” as seen in the sport of basketball.
By at least the 1920s, hustle came to mean “to defraud or swindle,” like a con job. In the 1940s in black slang, hustle signified a “paid job” (and legitimate one, at that) more generally. We have evidence for side hustle, or a source of money one has on the side of their main job, by the 1950s. Side hustle took off in the 2000s thanks to two forces: the internet and the gig economy.
The internet allowed people to earn money through projects on social media, such as making money on blogs or selling crafts on Etsy. The gig economy, like driving Uber or freelancing on Fiverr, allowed people more opportunities for a side hustle outside their main income.
To quote the infamous side hustler... "I got 2 jobs and a side hustle because that’s what it takes to get ahead in this economy". I just made that up! :)