Fetching details from the dictionary...

very; extremely; exceedingly; greatly; terribly
extreme; excessive; great many; large number of
splendid; impressive; tremendous; immense
exaggerated
彼は大そう喜んでプレゼントを受け取った。
He was extremely pleased when he received the gift.
今日は大そう冷え込んでいるので厚着をした。
It's extremely cold today, so I dressed warmly.
大そうな荷物を持って駅まで歩いた。
I walked to the station carrying an enormous load.