In an authoritative manner, being worthy of trust.(adverb)
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Use "authoritatively" in a sentence
"We want to make sure that you know what we know as authoritatively, as responsibly as we have it."
"Hereby the community or whole body of the faithful, even to the meanest member, are vested from Christ with full power and authority actually to discharge and execute all acts of order and jurisdiction without exception: e.g. To preach the word authoritatively, dispense the sacraments, ordain their officers, admonish offenders, excommunicate the obstinate and incorrigible, and absolve the penitent."
""'Enry," she called authoritatively, "stop teasing those girls, Hi say."