Otiose

otiose \ˈō-shē-ˌōs, ˈō-tē-\ adjective: 1. producing no useful result; futile, 2. being at leisure; idle, 3. lacking use or effect; functionless

Etymology: Latin otiosus, from otium leisure

I just read this word in a book. We can’t be familiar with all words, but sometimes I’m amazed to go through life without running into a word like otiose until now.