It is not Spanish but Latin, is pronounced skélsior, means "superior" and translates as excellent (closer to the original 'excelsus'). There is a Castilianization as an exélsior, but I have the impression that it was popularized from trademarks. As a curiosity, in English it is a way to call the chip precisely by the company that marketed it to fill packaging.
The word excelsior is written without accent or emphasis; of this form is contained in the main body of the DLE of the SAR. In English also written without accent or accent, clear. In some Latin American countries (Mexico p. ex.) ) it is written with accents and is registered in the Pan American Dictionary of idioms and voices.
