casco

As a noun helmet

is a protective head covering.

As a verb casco is

.

As nouns the difference between cisco and casco

is that cisco is any North American freshwater fish of the genus Coregonus that live in cold-water lakes while casco is a flat-bottomed, square-ended boat once used in the Philippines as a lighter to ferry goods between ship and shore.

As a proper noun Cisco

is cisco Systems, Inc., a manufacturer of routers, switches, and other networking and communications equipment.