The term 'Is Astir With Activity' can be summarized by the crossword solution 'Bustles', which is a 7-letter word. Bustles refer to a type of clothing accessory that was popular in the 19th century, consisting of a framework of hoops or stiffeners used to expand the fullness and support the drapery of a woman's skirt. The term 'bustles' has also come to mean a bustling activity or movement, suggesting a lot of activity and energy.