Final answer:
The word part that means weakness is -asthenia. It is derived from the Greek word "astheneia" and is found in words like neurasthenia and sarcopenia.
Step-by-step explanation:
The word part that means weakness is -asthenia.
This word part is derived from the Greek word "astheneia" meaning weakness or lack of strength.
Examples of words that contain this word part include neurasthenia (a condition characterized by fatigue and weakness) and sarcopenia (the gradual loss of muscle mass and strength).