It is a diacritical mark that is no longer used in Spanish, but is still visible in many languages (in esperanto). He is written with the character ^. Until early in the 19th century was used in Spanish about vowels preceded by an x, indicating that it had to pronounce as 'cs' and not as 'j'.
* Only one "like" per meaning and day, the more "likes" the meaning will appear higher in the list