Lowest part; ignoble (4)
I believe the answer is:
base
I believe this is a double definition.
'lowest part' is the first definition.
(I've seen this before)
'ignoble' is the second definition.
(similar in meaning)
(Other definitions for base that I've seen before include "Ignoble, military site" , "Plinth" , "Low kind of foundation" , "home?" , "Infamous" .)