Okay, so I just spent almost an hour reading up on some tequila drama that's spanned more than 50 years, perhaps even longer. And because of celebrity and social media, EVERYONE is an expert, don'-cha-know. Depending on who you ask, it all started with "The Long Goodbye", which was both lauded by critics as one of Raymond Chandler's best novels and reviled by critics as a second-rate "Farewell, My Lovel." In the 1953 novel, he said, "a real gimlet is half gin and half Rose's lime juice and nothing else."
However, mixologists of today, are peeking at original recipes that date from as early as 1852, which contradicts this and positions a gimlet as "containing gin, sugar, water and lime juice." Yet, because tequila wasn't imported (legally) to the US until the late 1880s by Don Cenobio Sauza, much of the "gin" of the day was actually tequila.
Therefore, despite the sordid drama surrounding the origins of who the inventor of the margarita was, which is heavily contested as between 1936 and the early 1950s, it is believed, by many that both the margarita and the gimlet are the same thing. But before you start running your mouth to your local bartender, be aware that the pool of those who most ardently disagree with this summation is about 40% (of those in-the-know).
Because of this, don't be surprised if--ordering both a margarita and a gimlet--you quickly discover that they taste nothing a like. And that's because gimlets (of today) are made with gin, and not tequila.
If you're just as thoroughly confused about this topic (or more so than when you first read this card), don't take it to heart. I am still reeling from it all. I never knew a cocktail like the margarita could boast so much drama in its origin, authenticity and alleged duplicity in history.