The term ATOP can be defined by the following crossword solutions: OVERHEAD (8 letters), ABOVE (5 letters), ONTO (4 letters), ON (2 letters), OVER (4 letters), and UPON (4 letters). ATOP is a preposition that means 'ON top of' or 'at the highest point of'. It is often used to describe the location of something, such as an object being placed ON top of another object. It can also be used to describe a person's position in relation to something else, such as being at the top of a mountain.