Other forms: testified, testifying, testifies
To testify is to give sworn evidence in court. Testify against him, called to testify, testified under oath.
The oath is what makes it testifying rather than telling, and lying under it is perjury. Figuratively, something testifies to a fact when it shows it: the crowds testify to his popularity. Note the Latin testis, a witness, plus facere, to make — so to testify is to make a witness of yourself.
1verbtestifyTo give sworn evidence in court.
“She agreed to testify against her former boss at the trial.”
2verbevidenceTo be evidence of something.
“Her many awards testify to her talent as a designer.”
Too few real examples of this word to estimate which sense is commonest.
testify is a giving of evidence.
Latin testificari is testis, a witness, plus facere, to make. Testimony, attest and protest come from the same witness.
Proto-Indo-European
*steh₂-
Latin
testificor — to bear witness
Old French
testifier
Middle English
testifien
English, today
testify
Built from
From Middle English testifien, borrowed from Old French testifier, from Latin testificor (“to bear witness”), from testis (“a witness”) + facere (“to make”). See -fy.
Etymology from Wiktionary, CC BY-SA