The term 'ADSORB' is a 6-letter solution to the crossword clue 'HOLD MOLECULES ON A SURFACE'. Adsorption is the process of molecules sticking to a surface, and is a type of surface phenomenon. It occurs when molecules in a gas or liquid state come into contact with a solid surface, and the molecules are held on the surface by weak forces. Adsorption is used in many industrial processes, such as water purification, and can also be used to separate mixtures of gases.