The adjective otiose means “useless”, “ineffective”, or “being at leisure”. It comes straight from that Latin word otiosus, “having leisure or ease, not busy”.
Merriam-Webster points out:
"There is also the noun form "otiosity," which predates "otiose" by approximately three centuries. That noun is rarely found in writing today, but it makes an appearance on the occasional spelling bee word list."
They’re right; I can’t find any example sentences for otiosity. But otiose shows up a few times on Google News, usually to mean “useless”. For example: “I will not be drawn into the miasma of premature analysis and debate, an otiose exercise” (David Hayford). Two vocab words in one sentence! What a deal! I’ll save miasma for next week. :)