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Nisr is Arabic for Eagle, Nasra/Nasr was the name of this Idol. He was shaped like an Eagle, however. His name is thought to come from Neshra, an idol shared with the people of Sheba. The name became Nashr, and finally Nasr/Nasra. This is all according to Ibn Al-Kalbi.  Source is mostly Arabic but it has some English references.
Thank you for the reference to al-Kalbi's Book of Idols! I fed the page above through Google Translate; couldn't understand most of it but I picked out a reference to the Talmud, which I then correlated to this English-language collection of "Talmudic miscellany": "There are five celebrated idolatrous temples, and these are the names of them:— The Temple of Bel in Babylon, the Temple of Nebo in Chursi, the Temple of Thretha in Maphog, the Temple of Zeripha in Askelon, and the Temple of Nashra in Arabia. When Rabbi Dimmi came from Palestine to Babylon he said there were others, viz., the Temple of Yarid in Ainbechi and that of Nad[-]bacha in Accho. (Avodah Zarah fol. 11 col. 2)" Unfortunately I don't know how to interpret that citation.