Part of nourishing piece of beef (4)
I believe the answer is:
shin
'piece of beef' is the definition.
(shin is a cut of beef)
'part of nourishing' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'SHIN' can be found hidden inside 'nourishing'.
(Other definitions for shin that I've seen before include "Part of the human leg" , "Cut of beef; part of leg" , "Climb" , "kick" , "bit of leg" .)