The Chinese word **急性** (jíxìng), meaning "acute" (as in a medical condition), is a compound formed by combining the character **急** (jí), meaning "urgent" or "rapid," with the character **性** (xìng), a suffix meaning "nature," "property," or "-ness." Therefore, the term is constructed through straightforward semantic composition: **急** conveys the quality of suddenness or severity, while **性** nominalizes it, creating a word that denotes the "nature of being rapid/urgent" — hence, describing a condition with a rapid onset and short, severe course, such as **急性肺炎** (acute pneumonia).