Which prefix means red?

• A. Erythr(o)
• B. Eti
• C. Em
• D. Encephal(o)

Answer: (A)

Prefixes that describe color in medical terms often come from Greek roots. Erythr(o) means red, derived from the Greek erythros. That makes it the correct choice because it appears in terms like erythrocyte (red blood cell) and erythroderma (reddened skin). The other options don’t denote color: eti- relates to cause or origin (etiology); encephal(o) refers to the brain; and em- isn’t a color prefix in medical terminology.