The phrase "that one" is a common way of referring to a specific thing or person. However, there are a variety of synonyms that can be used in its place. For example, the words "that individual," "that object," or "that item" can replace "that one" when describing something specific without using the word "one." Other options might include substituting "that thing," "that person," or "that item" in its place. Depending on the context and tone of a sentence, more colloquial options might include "that bad boy," "that lady," or "that thingamajig." By using a substitute for "that one," speakers can add variety and avoid repetition in their language.