https://www.merriam-webster.com/dictionary/gratuitous

gratuitous
ɡrəˈtjuːɪtəs/
adjective
adjective: gratuitous
1.
done without good reason; uncalled for.
"gratuitous violence"
synonyms:   unjustified, without reason, uncalled for, unwarranted, unprovoked, undue; More
antonyms:   justifiable, necessary
2.
given or done free of charge.
"solicitors provide a form of gratuitous legal advice"
synonyms:   free, gratis, complimentary, voluntary, volunteer, unpaid, unrewarded, unsalaried, free of charge, without charge, for nothing, at no cost, without payment; More
antonyms:   paid, professional