Cid \Cid\, n. [Sp., fr. Ar. seid lord.]

1. Chief or commander; in Spanish literature, a title of Ruy Diaz, Count of Bivar, a champion of Christianity and of the old Spanish royalty, in the 11th century.

2. An epic poem, which celebrates the exploits of the Spanish national hero, Ruy Diaz.

Source: Webster's Revised Unabridged Dictionary (1913)