Second-person singular simple present form of warn.(verb)
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Use "warnest" in a sentence
"Nothing can be more injudicious; for thou, my friend, who preachest to me that all the world is born perverse, warnest me that thou art born such also, and that I must mistrust thee as I would a fox or a crocodile."
"Seest thou not that thou warnest me that I do not try without resolving to conquer?"
"Eiðer of ow haueð his stunde to speokene. ne nis i {n} ckeR noðres tale to schunien in his time. þu warnest of wa. he telleð of wunne. muche neod is þ̵ me ow ba ȝeornliche hercni."