Form a mental image of is a phrase that refers to the ability to create a mental picture or representation of something in one's mind. ENVISAGE and IMAGINE are two words that can be used to describe this concept. ENVISAGE is an 8-letter word meaning to form a mental image of something, while IMAGINE is a 7-letter word meaning to form a mental image of something that is not real. Both words can be used to describe the same concept of forming a mental image of something.