If something has been definitely decided, the decision will not be changed. He told them that no venue had yet been definitely decided. without any doubt = certainly
without question and beyond doubt; "it was decidedly too expensive"; "she told him off in spades"; "by all odds they should win"
emphasis You use definitely to emphasize that something is the case, or to emphasize the strength of your intention or opinion. I'm definitely going to get in touch with these people `I think the earlier ones are a lot better.' --- `Mm, definitely.' = certainly