The term 'make more substantial' can be summarized by the crossword solution 'FATTEN, ' which is a six-letter word. To FATTEN something means to make it bigger, fuller, or more solid, usually by adding something to it. This term is often used in reference to food, such as when a farmer fattens their livestock before slaughter, but it can also be used to describe other things, such as making a story more substantial by adding more details.