1) Spanish language 
Castilian usually refers to something of, from, or related to Castile, including: ...
• (n.) An inhabitant or native of Castile, in Spain. • (n.) The Spanish language as spoken in Castile.
Cas·til'ian noun [ Spanish castellano , from Castila , New Latin Castilia , Castella . Castile, which received its name from the castles erected on the frontiers as a barrier against the Moors.] 1. An inhabitant or native of Castile, in Spain. 2. The Spani...
noun the Spanish language as spoken in Castile