It is not a noun: it is a reflexive singular pronoun.
We usually use this adjective with the verb to be: He was absent yesterday. Meaning that he sould have been there but was not. Also, we can use absent as a verb. He absented himself from the tiring gossip.
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.
Abstract noun of hopeless
The abstract noun is obligation.
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 noun childhood is a singular, common, abstract, compound noun; a word for the time of being a child.