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con·firm (kən-fûrm)
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tr.v. con·firmed, con·firm·ing, con·firms
1.
a. To support or establish the certainty or validity of; verify: confirm a rumor.
b. To reaffirm the establishment of (a reservation or advance arrangement).
2. To make firmer; strengthen: Working on the campaign confirmed her intention to go into politics.
3. To make valid or binding by a formal or legal act; ratify.
4. To administer the religious rite of confirmation to.

[Middle English confirmen, from Old French confermer, from Latin cōnfirmāre : com-, intensive pref.; see COM- + firmāre, to strengthen (from firmus, strong; see dher- in the Appendix of Indo-European roots).]

con·firma·bili·ty n.
con·firma·ble adj.
con·firma·tory (-fûrmə-tôrē) adj.
con·firmer n.

Synonyms: confirm, corroborate, substantiate, authenticate, validate, verify
These verbs mean to establish or support the truth, accuracy, or genuineness of something. Confirm implies the establishment of certainty or conviction: The information confirmed our worst suspicions.
To corroborate something is to strengthen or uphold the evidence that supports it: The witness is expected to corroborate the plaintiff's testimony.
To substantiate is to establish by presenting solid or reliable evidence: "What I shall say can be substantiated by the sworn testimony of witnesses" (Mark Twain).
To authenticate something is to establish its genuineness, as by expert testimony or documentary proof: Never purchase an antique before it has been authenticated.
Validate refers to establishing the validity of something, such as a theory, claim, or judgment: The divorce validated my parents' original objection to the marriage.
Verify implies proving by comparison with an original or with established fact: The bank refused to cash the check until the signature was verified.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

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