thankless
/ˈθæŋklɪs/adjective
1- (of a job or task) difficult or unpleasant and not likely to bring one pleasure or the appreciation of others（工作, 任务）吃力不讨好的, 不令人感激的, 不会带来乐趣的。
1.1
- (of a person) not expressing or feeling gratitude（人）不知感恩的, 忘恩负义的。
词源
thanklessly adverb, thanklessness noun.