List disheartened philosopher (4)
I believe the answer is:
heel
'list' is the definition.
(both can mean to lean or tilt)
'disheartened philosopher' is the wordplay.
'disheartened' means to remove the middle letters.
'philosopher' becomes 'hegel' (German philosopher Georg Wilhelm Friedrich Hegel).
'hegel' with its middle removed is 'HEEL'.
(Other definitions for heel that I've seen before include "One of the crusty ends of a loaf" , "one regarded with contempt" , "3's weak point" , "Contemptible person" , "Shoe part - come here, Fido!" .)