I am assuming that you mean "absolutely definitely" and "exactly" absolutely definitely - No room for doubt, the person agrees totally. exactly - this is not about agreement (although it can be used in that sense). It is about the correctness of what is said or done. There is a similar saying "spot on".

They are all very similar. 'Gushy' people who use lots of superlatives will often use two or more of them, just to avoid repeating themselves! ;^) The one difference is that you don't use 'not' after 'exactly'.