Abase oneself (6)
I believe the answer is:
grovel
'abase oneself' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for grovel that I've seen before include "Display abject humility" , "Cringe, be obsequious" , "Behave obsequiously in fear or servitude" , "Creep" , "Show extreme humility" .)