The word "in-effective" is often used to describe something that is lacking in achieving its intended purpose or goal. Some antonyms for this term could include "effective," "efficient," "productive," "powerful," and "successful." These words all convey the idea of something that is capable of achieving its intended result or purpose. Other antonyms for "in-effective" could include "strong," "potent," and "impactful," which suggest the capacity to have a significant effect or influence on something. These antonyms provide a range of options for expressing the opposite of "in-effective" and can help to add nuance and precision to our language use.