definitely (do something)
When you use "definitely", it means that you're sure. You use it to show how strongly you feel:
I definitely want to go.
"Definitely" is often used together with "can tell":
I can definitely tell that you've lost some weight.
You use "definitely" before a verb, but you can also use it before an adjective:
I'm definitely taller than him. He's like two inches shorter than me.