noun, noun or participle which takes 'suru'
major change; major transformation
Used for a significant, often dramatic change in state, situation, or appearance. Can be used as a noun or with する to mean 'to undergo a major change'.
この町はここ数年で大変化を遂げた。
This town has undergone a major transformation in the last few years.
彼の態度が急に大変
I was surprised when his attitude suddenly changed drastically.