The hotel fitness centre is definitely worth a visit.
I definitely need a holiday.
WORD CHOICE: WORD CHOICE: surely, definitely, certainly, naturally, be sure toUse surelyto say that you think something must be true, especially when other people do not agree• They should be there by now, surely.Use definitelyto say that something is certain to happen or be true• I will definitely be back (NOT I will surely be back) by ten. Use certainlyto emphasize that something is true• He certainly is (NOT surely is) a great cook.Use naturallyto mean 'as anyone would expect'• They were very late, so naturally I was (NOT surely I was) worried.Use be sure toto say that something is certain to happen• If you work hard you are sure to succeed (NOT you will surely succeed). ➔ See alsosurely
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.