The crossword solutions for the term ACTIVITY BUSY are HIVE, which is a four letter word. HIVE is a structure made by bees to store honey and house their colony. It is made up of hexagonal cells that are used to store honey and pollen, as well as to provide shelter for the queen bee and her offspring. The activity of the HIVE is very busy, as the bees are constantly flying in and out to collect nectar and pollen, and to build and maintain the HIVE.