Modus

wiktionary

ref

From Latin. Doublet of mode.

etymonline

ref

modus (n.)

"way in which anything is done," 1640s, from Latin modus (plural modi) "measure, extent, quantity; proper measure, rhythm, song; a way, manner, fashion, style," from PIE root *med- "take appropriate measures." Especially in modus operandi and modus vivendi.