mandate

1540–50; < Latin mandātum, noun use of neuter of mandātus, past participle of mandāre to commission, literally, to give into (someone's) hand. See manus, date¹

English mandate comes from Latin mandātum “an order, instruction, commission, imperial directive, (in law) a consensual contract.”
Mandātum is a neuter noun use of the past participle mandātus, from mandāre “to hand over, deliver, consign, entrust, delegate.” The first element of Latin mandāre is from the noun manus “hand”; the second part looks as if it were from dare “to give,” but in fact -dāre is a derivation of the combining form -dere “to put, place,” from a very widespread Proto-Indo-European root dhē-, dhō- “to place, set, put,” source of the English verb do. Mandāre therefore means “to put in the hands (of).”
Mandātum, via Old and Middle French mandé “washing of poor people’s feet during the Holy Thursday liturgy,” becomes maunde in Middle English and maundy in Modern English. Mandé, maunde, and maundy derive from the Vulgate Latin text of Jesus’ words during the Last Supper (Gospel of St. John, 13:34): Mandātum novum dō vōbis, ut diligātis invicem “A new commandment I give unto you, that ye love one another.”