na-adjective, noun
exaggerated; extravagant; overdone
Often used sarcastically or critically to describe something as overly grand, dramatic, or excessive. The honorific ご adds a mocking tone.
彼の話はいつもご大層で、信じられない。
His stories are always exaggerated and hard to believe.
そんなご大層な計画、実現できるわけがない。
There's no way such an extravagant plan can be realized.
大げさ is a more common and neutral word for 'exaggerated' or 'overstated', while ご大層 carries a sarcastic or mocking nuance due to the honorific prefix.
Combination of the honorific prefix ご and 大層 (たいそう, 'very', 'greatly'). The prefix adds a sarcastic or mocking tone, turning the meaning toward 'exaggerated' or 'overdone'.