Which prefix means 'Half'?

• A. Exo-
• B. Retro-
• C. Semi-
• D. Intra-

Answer: (C)

The main idea being tested is recognizing a prefix that conveys half or partial meaning. Semi- is the prefix that means half, partial, or incomplete. It appears in terms like semicircle (half a circle), semicomatose? Actually semicomatose would be partially conscious; semipermeable describes a membrane that allows some substances to pass. This direct sense of half or partial is what semi- communicates in medical terminology.

Exo- means outside or outer, retro- means backward or behind, and intra- means within or inside. Those meanings don’t align with half, so semi- best fits the concept being asked.