Casual pressure breaking shoulder-bone (7)
I believe the answer is:
scapula
'shoulder-bone' is the definition.
(I've seen this before)
'casual pressure breaking' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'breaking' indicates an anagram.
'casual'+'p'='casualp'
'casualp' is an anagram of 'SCAPULA'.
(Other definitions for scapula that I've seen before include "Shoulder-bone" , "Flat, triangular human bone - cap Saul (anag)" , "Shoulder-blade" , "Shoulder blade" .)