noun, noun or participle which takes 'suru', intransitive verb
disillusionment; disenchantment
The feeling of disappointment when something turns out to be less ideal than expected. Often used with する to mean 'become disillusioned'.
彼の行動に幻滅した。
I was disillusioned by his behavior.
理想と現実のギャップ
I feel disillusionment at the gap between ideals and reality.