No, the word 'busiest' is the superlative form of the adjective busy (busier, busiest).
The abstract noun form of the adjective 'busy' is business.
The adjective busy has the abstract noun busyness, which became used as the separate word "business" to refer to occupational and commercial activity.
Yes, the noun astonishment is an abstract noun, a word for an emotional reaction.
Is undergone an abstract noun
Concrete noun
The abstract noun is criticism.
The noun 'hopefulness' is an abstract noun, a word for an emotion.
The abstract noun is obligation.
Abstract noun of hopeless
Friendship has not abstract noun because It is a abstract noun
The abstract noun form is tourism.
The abstract noun for the adjective vacant is vacantness. Another abstract noun form is vacancy.
The abstract noun for the adjective quick is quickness.