Through all the horrible conquests and murders Thanos has committed through blind ambition for a better world, he does have one ounce of humanity with Gamora, as seen in Avengers: Infinity War. Would this alone be enough to label him as an anti-villain?
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It really depends on your definition, but yes, it is possible to describe him in this way.
And Anti-Villain can be defined as "a villain with heroic goals, personality traits, and/or virtues" and Thanos fits into this. Although we shouldn't dismiss the "Villain" part, he has good intentions and is at his heart just trying to do what he believes is best for the universe (even if it's not what's actually best for the universe)