Jastrow's iconic Dictionary of the Targumim, Talmud Bavli, Talmud Yerushalmi and Midrashic Literature is outdated in many ways, but remains useful if consulted judiciously. I see from the archives that I have cited it on PaleoJudaica off and on over the years. You can already find it online (e.g., here, here, and here) and it remains in print, but it sounds as though the Sefaria version has been prepared with special care.
Background on the Sefaria website is here and links.
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