Certainly, absolutely, as a matter of course, absolutely, and by all means are all synonyms for definitely. Possibly and doubtfully are antonyms of definitely. And here are 55 another word for definitely.
Absolutely, assuredly, beyond any doubt, by a mile, categorically, certainly, clearly, decidedly, easily, far and away, for sure, incontestably, incontrovertibly, indubitably, irrefutably, needless to say, obviously, palpably, patently, plainly, positively, surely, there are no two ways about it, there's no denying it, transparently, undeniably, undoubtedly, unequivocally, unmistakably, unquestionably, without fail, without/beyond doubt, without/beyond question, and as sure as eggs is eggs are all synonyms for definitely.
As a matter of course, as might be expected, as was anticipated, as you/one would expect, certainly, clearly, it goes without saying, naturally, needless to say, not unexpectedly, obviously, to be sure, and natch are all another word for definitely.
Absolutely, by all means, certainly, definitely, with pleasure, yes, and sure thing are all synonyms for definitely.
Definitely synonym page has a variety of synonyms that differ in length. 1 synonym with 3, 15, 18, 21, and 24 letters and 2 synonyms with 6, 12, 14, 16, and 19 letters. 5 synonyms with 7 letters and 3 synonyms with 8, and 17 letters.
8 synonyms with 9 letters and 7 synonyms with 10 letters. 4 synonyms with 11 letters and 6 synonyms with 13 letters. For a total of 51 another word for definitely.
I will definitely join you.
She is definitely the best.
This project will definitely succeed.
I definitely agree with you.