An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The generic name applied to books in Arabic and Persian that tabulate parameters used for astronomical calculations of positions of the Sun, the Moon, and the five planets of antiquity. Some examples: Zij al-Sindhind, by Khwarizmi (c. 780-850), Az-Zij as-Sabi by al-Battâni (Albatenius) (853-929), Zij-i Ilkhâni by Nassireddin Tusi (1201-1274), Zij-i Sultâni by Ulugh Brg (1437), → Toledan Tables, → Alfonsine Tables.

The word is derived from Mid.Pers. zig, variant zih "cord, string" (Mod.Pers. zeh "cord, string"); Av. jiiā- "bow-string," cognate with Skt. jiyā- "bow-string," PIE base *g^whi- "thread, tendon" (from which derive also Gk. bios "bow", L. filum "thread", Russ. žca "thread").
The term zig originally referred to the threads in weaving, but because of the similarity between the rows and columns of astronomical tables and the parallel threads, it came to be used for an astronomical table, and subsequently a set of tables.