The antonym for the word "more massed" is "less crowded." When something is more massed, it means that there is a larger group or collection of items that are densely packed together. On the other hand, when something is less crowded, it means that there are fewer items in a given space, and as a result, they are more spread out. This could refer to anything from a group of people in a room to a collection of books on a shelf. Having something less massed can lead to a feeling of more openness and breathing room which can be both physically and mentally beneficial.