gratuitous

Concise Oxford English Dictionary © 2008 Oxford University Press:
gratuitous /grəˈtjuːɪtəs/

▶adjective

• 1 done without good reason: gratuitous violence.

• 2 free of charge.

– derivatives
gratuitously adverb,
gratuitousness noun.

– origin C17: from L. gratuitus ‘given freely, spontaneous’ + -ous.