Penny is mistaken, ignoring initial sticking point (5)
I believe the answer is:
prong
'sticking point' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for prong that I've seen before include "Spike of fork etc" , "branch" , "tip?" , "Tooth" , "Pointed end of fork" .)