Knight, slippery type entertained by monarch, is showing obeisance (8)
I believe the answer is:
kneeling
'showing obeisance' is the definition.
(obeisance is showing respect to a superior)
'knight slippery type entertained by monarch' is the wordplay.
'knight' becomes 'N' (abbreviation for knight in chess).
'slippery type' becomes 'eel' (eels are slippery).
'entertained by' indicates putting letters inside (I've seen this in other clues).
'monarch' becomes 'king' (king is a kind of monarch).
'n'+'eel'='neel'
'neel' placed into 'king' is 'KNEELING'.
'is' is the link.
(Other definitions for kneeling that I've seen before include "Position for being knighted or proposing?" , "On one's knees" , "In a prayerful position" .)