gratuitous (adj) – free or offered without charge; unjustified; unnecessary; without reason, cause, or proof
BREAKDOWN: GRAT- (favor) + -OUS (full of)
— a gratuity is a tip or reward of money; something offered freely and without obligation
This word is built on the root GRAT-, which means thanks, favor, or pleasing.
Common GRAT- words include include agree, grateful, gratitude, greet, and greeting.
More esoteric GRAT- words include gratuitous.