surely
[adverb]
Synonyms: undoubtedly, certainly, definitely, doubtlessly, indubitably, unquestionably, without doubt

[TahlilGaran] English Synonym Dictionary ▲

sure‧ly S1 W2 /ˈʃɔːli $ ˈʃʊrli/ adverb

1. [sentence adverb] used to show that you think something must be true, especially when people seem to be disagreeing with you:
You must have heard about the riots, surely?
There must surely be some explanation.
Surely we can’t just stand back and let this happen?

2. surely not spoken used to show you cannot believe that something is true:
‘The chairman’s just handed in his resignation.’ ‘Surely not.’

3. formal certainly:
Such sinners will surely be punished.

4. American English old-fashioned used to say ‘yes’ to someone or to express agreement with them
⇒ slowly but surely at slowly(2)

[TahlilGaran] Dictionary of Contemporary English ▲

surely
adverb
1.
BAD: It was an absolutely terrible flight. The next time I go to Rio, I will surely go by train.
GOOD: It was an absolutely terrible flight. The next time I go to Rio, I will definitely go by train.

Usage Note:
Surely is used to express a strong belief in the truth or likelihood of what you are saying, and often to encourage the listener to express agreement: 'Surely they should have arrived by now!' 'A twenty-dollar parking fine! Surely someone's made a mistake!' 'You don't need to wear a coat in this weather, surely?'
Definitely expresses a sense of complete certainty about something: 'She said she'd definitely be back by dinner time.' 'This is definitely the best film she's ever made.'

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2.
BAD: On the first day we'll just stay at the hotel and rest because the journey will be surely tiring.
GOOD: On the first day we'll just stay at the hotel and rest because the journey is bound to be tiring.

Usage Note:
If you feel sure that something is going to happen, you say that it is bound/sure to happen: 'At the interview they're bound to ask you about your last job.' 'Once drivers get impatient, accidents are sure to happen.'

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3.
BAD: He said he felt worried because of all the recent air disasters. Surely I became worried too.
GOOD: He said he felt worried because of all the recent air disasters. Naturally I became worried too.

Usage Note:
When you mean 'as anyone would expect', use naturally or of course : 'She's just lost her job and so naturally she's feeling a bit depressed.' 'Henry is still in France but he'll be back in time for the wedding of course.'

[TahlilGaran] Dictionary of Common Errors ▲