From the Latin words "fonte seca" meaning "dry well" referencing a person that lived near a spring that dried up during the summer months. This surname originates from Spain, Portugal, and Italy. Members of Fonseca enjoyed the title of Marquis in Spain - and in Venice accumulated great wealth. This distinguished family holds Coat of Arms in the three aforementioned countries.
This surname is also common amongst Sephardic Jews. Basically, people with this last name are badass.
Did you check out Fonseca's family crest? It just "breathes" nobility.