What does the prefix a- mean?

• A. toward
• B. without
• C. away from
• D. to, in the direction of

Answer: (B)

The prefix a- in medical terms signals absence or lack of something. It’s a negating prefix, so it turns a root concept into its opposite or into “not.” That’s why apnea means without breath, anemia means without enough blood, and amnesia means without memory. This prefix isn’t about direction like toward or away from—that use comes from other prefixes such as ad- (toward) or ab- (away from). So the best meaning is “without.”