The word 'in apter' doesn't actually exist in the English language, but if we assume it is meant to be 'inepter,' the antonyms could be 'apt' or 'competent.' Both these words mean having the necessary knowledge, skills, or abilities to do something successfully. In contrast, 'inept' means lacking in skill or ability and making mistakes. Some other antonyms for 'inept' could be 'skillful,' 'proficient,' or 'adept.' The opposite of 'inept' can also be expressed through the phrase 'adequate' or 'capable,' which indicate a level of proficiency that is satisfactory enough to accomplish a task.