The antonyms for the word "in efficient" are "efficient," "effective," "productive," and "proficient." When something is efficient, it means that it is able to perform its functions with the least amount of waste or inefficiency. In contrast, something that is inefficient is slow, ineffective, and sometimes wasteful. Effective means that something achieves its intended purpose, successful in producing a desired result. While productive means that something is able to produce desirable results or output. A proficient process or individual demonstrates competence and expertise in performing a particular job or task. By knowing the antonyms for inefficiency, one can easily identify and implement the best practices towards a more efficient and productive day.