Pull and snap uncovered bone (4)
I believe the answer is:
ulna
'bone' is the definition.
(ulna is a kind of bone)
'pull and snap uncovered' is the wordplay.
'pull' becomes 'ul' (I can't justify this - if you can you should believe this answer much more).
'and' says to put letters next to each other.
'uncovered' says to take the centre.
The centre of 'snap' is 'na'.
'ul'+'na'='ULNA'
Can you help me to learn more?
(Other definitions for ulna that I've seen before include "a section of framework" , "Part of bone-structure" , "Part of body" , "The longer and inner bone in forearm" , "One of two bones of the forearm" .)