Synonyms for Gratuitous (same or very similar meaning)
WordNet sense 1 (costing nothing):
complimentary, free, gratis, costlessWordNet sense 2 (unnecessary and unwarranted):
needless, uncalled-forWordNet sense 3 (not necessary):
unnecessaryWordNet sense 4 (not merited or deserved):
unmeritedFrom the ODE community, based on WordNetadd/edit