Which combining form means 'smooth'?

• A. Amyl/o
• B. Lact/o
• C. Caud/o
• D. Lei/o

Answer: (D)

Recognize that combining forms carry specific meanings from Greek or Latin. The form that means smooth comes from Greek leios, giving lei/o- as the combining form. This appears in terms like leiomyoma (a tumor of smooth muscle) and leiomyopathy, where the sense of smooth is the key idea. The other roots point to entirely different substances: amyl/o means starch, lact/o means milk, and caud/o means tail. So the combining form for smooth is lei/o.