CERTAINLY
surely, certainly, sure, for sure, for certain, sure enough, sure as shooting
(adverb) definitely or positively (‘sure’ is sometimes used informally for ‘surely’); “the results are surely encouraging”; “she certainly is a hard worker”; “it’s going to be a good day for sure”; “they are coming, for certain”; “they thought he had been killed sure enough”; “he’ll win sure as shooting”; “they sure smell good”; “sure he’ll come”
Source: WordNet® 3.1
Etymology
Adverb
certainly (comparative more certainly, superlative most certainly)
In a way which is certain; with certainty.
Without doubt, surely.
An emphatic affirmative answer; of course.
Synonyms
• (with certainty): absolutely, beyond doubt, indubitably, sure thing, undoubtedly, wis (obsolete), without a doubt
• (without doubt): definitely, doubtlessly, in fact, indeed, indisputably, indubitably, no doubt, really, sure, surely, truly, undoubtedly, unquestionably, wis (obsolete), without a doubt
• (emphatic affirmative): damn right, damn straight, fo shizzle, for sure, oh yeah, wye aye (dialect)
Coordinate terms
• maybe, possibly, arguably, questionably, probably, perhaps
Source: Wiktionary
Cer"tain*ly, adv.
Definition: Without doubt or question; unquestionably.
CERTAIN
Cer"tain, a. Etym: [F. certain, fr. (assumed) LL. certanus, fr. L.
certus determined, fixed, certain, orig. p. p. of cernere to
perceive, decide, determine; akin to Gr. concern, critic, crime,
riddle a sieve, rinse, v.]
1. Assured in mind; having no doubts; free from suspicions
concerning.
To make her certain of the sad event. Dryden.
I myself am certain of you. Wyclif.
2. Determined; resolved; -- used with an infinitive.
However, I with thee have fixed my lot, Certain to undergo like doom.
Milton.
3. Not to be doubted or denied; established as a fact.
The dream is certain, and the interpretation thereof sure. Dan. ii.
45.
4. Actually existing; sure to happen; inevitable.
Virtue that directs our ways Through certain dangers to uncertain
praise. Dryden.
Death, as the Psalmist saith, is certain to all. Shak.
5. Unfailing; infallible.
I have often wished that I knew as certain a remedy for any other
distemper. Mead.
6. Fixed or stated; regular; determinate.
The people go out and gather a certain rate every day. Ex. xvi. 4.
7. Not specifically named; indeterminate; indefinite; one or some; --
sometimes used independenty as a noun, and meaning certain persons.
It came to pass when he was in a certain city. Luke. v. 12.
About everything he wrote there was a certain natural grace und
decorum. Macaulay.
For certain, assuredly.
– Of a certain, certainly.
Syn.
– Bound; sure; true; undeniable; unquestionable; undoubted; plain;
indubitable; indisputable; incontrovertible; unhesitating;
undoubting; fixed; stated.
Cer"tain, n.
1. Certainty. [Obs.] Gower.
2. A certain number or quantity. [Obs.] Chaucer.
Cer"tain, adv.
Definition: Certainly. [Obs.] Milton.
Source: Webster’s Unabridged Dictionary 1913 Edition