Mr Domingo lacks nothing, and is calm (6)
I believe the answer is:
placid
'is calm' is the definition.
(similar in meaning)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for placid that I've seen before include "Unexcitable" , "not easily angered" , "Calm and tranquil" , "Composed or serene" , "Calm and not easily upset" .)