The word "回味无穷" is formed by combining the two-character phrase "回味", meaning "aftertaste" or "to recall the taste", with "无穷", meaning "endless". "回味" itself is a verb-object construction from "回" (to recall) and "味" (taste), while "无穷" is a negation phrase from "无" (without) and "穷" (end). These are joined in a subject-predicate structure where "回味" acts as the subject and "无穷" as the predicate, literally stating that the aftertaste has no limit.