The term 'sturdy fastener' can be summarized by the crossword solution 'RIVET, ' which is a five-letter word. A RIVET is a type of mechanical fastener that is used to join two or more pieces of material together. It is made up of a cylindrical body with a head on one end and a tail on the other. The tail is inserted through the two pieces of material and then the head is hammered down, creating a strong bond. Rivets are commonly used in construction, automotive, and aerospace industries due to their strength and durability.