Synonyms for Modus operandi:

n.

tactic, tack, line, course, attack, plan, basis, means, technique, approach. method, system, wise, manner, way, mode, style, fashion. act (noun)
routine.
approach (noun)
manner, way.
manner of operating (noun)
technique, system, way, means, approach, method, manner.
method (noun)
technique.
modus operandi (noun)
routine.

Other synonyms:

system, technique. way, method, mode, manner, tack. plan, style. fashion. course. line. Other relevant words:
technique, approach, line, plan, course, mode, means, style, tack, attack, system, wise, method, way, fashion, manner.