Aruch

Written by Rav Natan the son of Yechiel, who lived in Rome from 1035 until 1106. The Aruch can perhaps be classified as a scholarly Talmudic dictionary, tracing the root of each word and citing the text in which it appears. It draws off of the works of several Geonim and early Rishonim, and was accepted by both Ashkenazic and Sephardic authorities