The term "in-fix" refers to a distinguishing element that is affixed or inserted within a word, phrase or sentence. Antonyms of "in-fix" include words like suffix and prefix, which are also elements that are affixed to words, but they are attached either at the beginning or at the end, respectively. Other antonyms of "in-fix" could include words like delete, eliminate, remove, or detach, as they all involve the act of taking away or separating something. Furthermore, antonyms like exterior, outside, or peripheral could be used to describe elements that are not affixed or included within a word or sentence.