Lower the dignity of (6)
(Other definitions for humiliate that I've seen before include "Abash" , "Crush" , "To humble" , "Put down" , "Deprive of dignity, make to feel ashamed" .)
'lower the dignity of' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for demean that I've seen before include "Belittle; degrade" , "Lower in dignity or reputation" , "Lower in status or reputation" , "Humble" , "Cause (someone) to lose dignity" .)