Mandatory

google

ref

late 15th century: from late Latin mandatorius, from Latin mandatum ‘something commanded’.

wiktionary

ref

From Late Latin mandatorius(“of or belonging to a mandator”), from mandator(“one who commands”); see mandate.

etymonline

ref

mandatory (adj.)

1570s, "of the nature of a mandate, containing a command," from Late Latin mandatorius "pertaining to a mandator" (one who gives a charge or command), from Latin mandatus, past participle of mandare (see mandate (n.)). Sense of "obligatory because commanded" is from 1818.