The word "unfunctional" represents the opposite of something that is useful, efficient, or effective. To express an idea that is contrary to unfunctional, one can use antonyms such as "functional," "operational," "working," "useful," "efficient," "productive," "practical," "effective," and "helpful." These words imply that something is in good condition, works as intended, or fulfills its purpose. They reflect positivity, and use of these antonyms shows that something is not only working, but that it works exceptionally well. When choosing an antonym for unfunctional, it is important to remember to select a word that accurately reflects the intended meaning.