IPA: /ˈbuːt.ləs.li/
KK: /ˈbutlɪsli/
In a way that is useless or without success.
He tried to convince her bootlessly, as she had already made up her mind.
Bootlessly → It is formed from "boot" (from Old English *bōt*, meaning remedy or compensation) and the suffix "-less" (meaning without). The word "bootlessly" means without remedy or compensation.
Think of 'boot' as a remedy or compensation, and remember that 'bootlessly' means without that remedy.