As a result, king lacking self-confidence (3)
I believe the answer is:
ego
'self-confidence' is the definition.
(I've seen this before)
'as a result king lacking' is the wordplay.
'as a result' becomes 'ergo' (therefore).
'king' becomes 'R' (abbreviation for rex, king in Latin).
'lacking' suggests deleting specific letters.
'ergo' with 'r' removed is 'EGO'.
(Other definitions for ego that I've seen before include "Self-esteem, conceit" , "In Virgil I" , "Part of the mind" , "Aspect of the personality" , "Selfishness" .)