The name used in the Cantar de Mio Cid is Tizón.
The form Tizona has been in use since the late medieval period (14th century).
The blade inscription on the Marcilla sword, presumably of the 13th or 14th century, has the form TIZONA.
The older form of the name, tizón, is a word for "firebrand" (leño encendido, from Latin titionem).
Sebastián de Covarrubias (1611) recognizes this as the plausible origin of the name Tizona, but also adduces possible derivation from τυχωνα, the name of the lance of Severus Alexander, or from τύχη "fortuna".
James I of Aragon (r. 1213–1276) according to the Llibre dels fets had a sword named Tisó. The description of this sword makes no reference to El Cid, suggesting that tizon "firebrand" was in use as a generic term for "sword" (c.f. the same use of English brand).
The extended (feminine) form tizona, by reference to El Cid's sword, could later also stand in as a poetic synonym of "sword" in general.