Porous breastbone almost shattered (9)
I believe the answer is:
absorbent
'porous' is the definition.
(I've seen this before)
'breastbone almost shattered' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'shattered' indicates an anagram.
'breastbone' with its last letter taken off is 'breastbon'.
'breastbon' with letters rearranged gives 'ABSORBENT'.
(Other definitions for absorbent that I've seen before include "receptive" , "Porous" , "Able to mop up" , "Bob ran set (anag.)" , "taking everything in?" .)