The term 'close link' can be defined as a BOND between two people or entities. The crossword solution for this term is 'BOND', which is a four-letter word. A BOND is a strong connection that binds two people or entities together, and it can be either physical or emotional. Bonds are often formed through shared experiences, such as friendship, family, or work. Bonds can also be formed through mutual interests, such as hobbies or sports. Bonds can be strengthened over time, and they can be broken if the relationship is not nurtured.