Open to attack from a bull? Nerve shattering (10)
I believe the answer is:
vulnerable
'open to' is the definition.
(similar in meaning)
'a bull? nerve shattering' is the wordplay.
'shattering' indicates an anagram.
'a'+'bull'+'nerve'='abullnerve'
'abullnerve' is an anagram of 'VULNERABLE'.
'attack from' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for vulnerable that I've seen before include "Exposed" , "Susceptible" .)