It sticks out and sticks in (4)
I believe the answer is:
spur
'it sticks out and sticks in' is the definition.
The definition suggests a singular noun which matches the answer.
This is the entire clue.
Can you help me to learn more?
(Other definitions for spur that I've seen before include "Branch - incitement" , "Sharply pointed projection" , "Rider's heel wheel" , "Goad as for use by horse-rider" , "branch road" .)