/ ˈsɜːtnli; NAmE ˈsɜːrtnli/ adverb
1.
without doubt
SYN definitely :
Without treatment, she will almost certainly die.
Certainly, the early years are crucial to a child's development.
I'm certainly never going there again.
➡ note at surely
2.
(used in answer to questions) of course :
'May I see your passport, Mr Scott?' 'Certainly.'
'Do you think all this money will change your life?' 'Certainly not.'