Inefficacious is a related term of inoperative.
As adjectives the difference between inefficacious and inoperative
is that inefficacious is incapable of having the intended consequence while inoperative is not working or functioning; either idle or broken.
inefficacious
English
Adjective
(
en adjective)
Incapable of having the intended consequence.
Not effective.
Synonyms
* ineffective
inoperative
English
Adjective
(-)
not working or functioning; either idle or broken
(legal) No longer legally binding