To humble (6)
I believe the answer is:
demean
'to humble' is the definition.
(I know that demean is a more specific form of the action abase)
This is all the clue.
(Other definitions for demean that I've seen before include "Belittle; degrade" , "Reduce in worth" , "Degrade, humiliate" , "disgrace" , "Lower, degrade" .)