The term 'FALL VERTICALLY' can be solved by the crossword solution 'DROP', which is a four-letter word. The term 'FALL VERTICALLY' refers to the act of falling in a straight line, usually from a higher point to a lower one. This is a common occurrence in nature, such as when raindrops fall from the sky or when leaves fall from trees. It is also used to describe the motion of objects in physics, such as when an object is dropped from a certain height.