U

for certain

adjective

free from doubt or reservation; confident; sure: I am certain he will come.
destined; sure to happen (usually followed by an infinitive): He is certain to be there.
inevitable; bound to come: They realized then that war was certain.
established as true or sure; unquestionable; indisputable: It is certain that he tried.
fixed; agreed upon; settled: on a certain day; for a certain amount.
definite or particular, but not named or specified: A certain person phoned. He had a certain charm.
that may be depended on; trustworthy; unfailing; reliable: His aim was certain.
some though not much: a certain reluctance.
Obsolete. steadfast.

pronoun

certain ones: Certain of the members declined the invitation.

Idioms

for certain, without a doubt; surely: I know for certain that I have seen that face before.

adjective

(postpositive) positive and confident about the truth of something; convincedI am certain that he wrote a book
(usually postpositive) definitely knownit is certain that they were on the bus
(usually postpositive) sure; bound; destinedhe was certain to fail
decided or settled upon; fixedthe date is already certain for the invasion
unfailing; reliablehis judgment is certain
moderate or minimumto a certain extent
make certain of to ensure (that one will get something); confirm

adverb

for certain definitely; without a doubthe will win for certain

determiner

1. known but not specified or namedcertain people may doubt this
2. (as pronoun; functioning as plural)certain of the members have not paid their subscriptions
named but not knownhe had written to a certain Mrs Smith

adj.

c.1300, “determined, fixed,” from Old French certain “reliable, sure, assured” (12c.), from Vulgar Latin *certanus, from Latin certus “sure, fixed, settled, determined” (also source of Italian certo, Spanish cierto), originally a variant past participle of cernere “to distinguish, decide,” literally “to sift, separate” (see crisis).

Of persons, “full of confidence in one’s knowledge or judgment,” from mid-14c. Euphemistic use (of a certain age, etc.) attested from mid-18c. Certainer, certainest were common to c.1750, but have fallen from proper use for some reason. Expression for certain “assuredly” is attested by early 14c.

Also, for sure. Without doubt. For example, I can’t tell for certain if this is the right color, or I know for sure that she has a new car. The first term dates from the early 1300s. The variant, dating from the late 1500s, is also used colloquially to express agreement or assert the truth of a statement, as in Mary is really bossy.—That’s for sure, or Are you coming to the party?—For sure I am.

see for certain.