Dishonourable (7)
'dishonourable' is the definition.
(similar in meaning)
This is the entire clue.
(Other definitions for ignoble that I've seen before include "Contemptible" , "I belong to low sort" , "No bilge! (anag)" , "'Base, dishonourable (7)'" , "I belong to base sort" .)
(Other definitions for lowdown that I've seen before include "Dope" , "facts" , "Data" , "confidential information" , "news" .)