Gratuitous

google

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mid 17th century: from Latin gratuitus ‘given freely, spontaneous’ + -ous.

wiktionary

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From Latin grātuītus(“free”), from Latin grātia(“favor”), grātus(“showing favor”)

etymonline

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gratuitous (adj.)

1650s, "freely bestowed," from Latin gratuitus "done without pay, spontaneous, voluntary," from gratus "pleasing, agreeable," from gratia "favor" (from suffixed form of PIE root *gwere- (2) "to favor"). Earlier was gratuital (1590s). Sense of "uncalled for, done without good reason" is first recorded 1690s.