1
general::
1. Probably, most likely, as in No doubt you've heard the news about Mother. [Early 1300s] 2. Also, without doubt or a doubt. Certainly, without question, as in He's guilty, no doubt, but he doesn't deserve such a long sentence, or That basketball player is without doubt the tallest man I've ever seen. [Early 1300s] Also see BEYOND A DOUBT.
American Heritage Idioms
2
general::
Phrase(s): no doubt
a transitional or interpretative phrase strengthening the rest of a previous sentence. • Sue: Mary is giving this party for herself ? Rachel: Yes. She’ll expect us to bring gifts, no doubt. • Mary: All this talk about war has my cousin very worried. Sue: No doubt. At his age, I don’t wonder.
McGrawhill's American Idioms And Phrasal Verbs