mor ‧ tal ‧ ly /ˈmɔːt ə l-i $ ˈmɔːr-/ BrE AmE adverb
1 . in a way that will cause death SYN fatally :
He regarded the mortally wounded man with no pity in his heart.
2 . extremely or greatly:
He was mortally afraid of upsetting her.
I tried to be tactful, but he seemed to be mortally offended.