Chair joint sounds weak (4)
I believe the answer is:
puny
'weak' is the definition.
(similar in meaning)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for puny that I've seen before include "Small and feeble" , "Paltry" , "Weak - unimportant" , "in need of development" , "Insignificant" .)