Nathan ben Jehiel of Rome (Hebrew: נתן בן יחיאל מרומי, romanized: Nāṯān ben Yəḥiʾel mirRomi, c. 1035 – 1106) was a Jewish Italian lexicographer. He authored the Arukh, a dictionary for Rabbinic Judaism that was the first work to examine Jewish Babylonian Aramaic. He is therefore referred to as "the Arukh."

Nathan was born in Rome not later than 1035 to one of the most notable Roman families of Jewish scholars. Owing to an error propagated by Chaim Yosef David Azulai, he has been regarded as a scion of the house of de Pomis. However, according to present scholarship, it is almost a certainty that he belonged to the Anaw (ענו, Italian: degli Mansi) family. Aside from being an acknowledged authority on halakha, Nathan's father, Jehiel ben Abraham, was a liturgic poet like most contemporary Italian rabbis.

The details of Nathan's sad life must be excerpted and pieced together from several autobiographic verses appended to the first edition of his lexicon. It appears that he began life not as a student but as a peddler of linenwear, which was then considered a distasteful occupation. The death of his employer caused him to abandon trade for the Torah. He returned home, where his father began to bestow upon him the treasures of learning, the accumulation of which was continued under foreign masters.

Nathan went to Sicily. Maṣliaḥ ben Eliah al-Baṣaq had just returned from a course of study under Hai ben Sherira, the last gaon of Pumbedita Academy in Baghdad in Lower Mesopotamia. Nathan learned these traditions, leading some to the erroneous notion that he had himself pilgrimed to Pumbedita.

Then Narbonne enticed him, where he sat under the prominent exegete and aggadist Moshe ha-Darshan. On his way home, he probably lingered for a while at the several academies flourishing in Italy, notably at Pavia, where a rabbi named Moses was headmaster, and at Bari, where Moses Kalfo taught. He arrived home from his scholarly travels sometime before his father's death, which occurred about 1070 and allowed him to illustrate the simplicity of funeral rites he had advocated.

The Roman community entrusted the rabbinic college's presidency to Jehiel's three learned sons: Daniel, Nathan, and Abraham – 'the geonim of the house of Rabbi Jehiel', as they were styled. Daniel, the eldest, seems to have composed a commentary on the Mishnaic section Zeraim, from which the Arukh quotes frequently and to have stood in friendly relations with Christian scholars. The three brothers rapidly acquired general recognition as authorities on the Torah, and numerous inquiries were addressed to them. Their most frequent correspondent was Solomon ben Isaac ("Yitzhaki"), an Italian scholar.

Nathan's private life was unfortunate. All his children died very young, and he sought solace in philanthropy and scholarly application. In the year 1085, he built a mikva, and about seventeen years later, in September 1101, he and his brothers erected a synagogue. In February 1101, he completed the Arukh.

The sources of this work are numerous. Aside from the Arukh of Tzemach ben Poltoi, which he utilized (it should be stated, however, that Solomon Judah Loeb Rapoport and Abraham Geiger deny this), he used a vast number of additional works. Above all, he placed under contribution the information received, in both oral and written form, from R. Maẓliaḥ and R. Moses ha-Darshan, the former of whom, in particular, through his studies under Hai, had made himself the repository of Eastern learning. The entire extent of Nathan's indebtedness to his authorities can not be estimated because of the hundreds of books he cited, many of which have not been preserved. But none will deny his obligation to Gershom ben Judah, whom he repeatedly quotes, though, as Kohut rightly maintains against Rapoport, he can not have been his disciple.