Self-confidence registered, even spread round (5)
I believe the answer is:
nerve
'self-confidence' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'registered even spread round' is the wordplay.
'registered' becomes 'R' (abbreviation, as in registered trademark).
'spread' indicates anagramming the letters.
'round' means one lot of letters goes inside another.
'even' anagrammed gives 'neve'.
'r' going into 'neve' is 'NERVE'.
Can you help me to learn more?
(Other definitions for nerve that I've seen before include "Impudence (colloq.)" , "Coolness under fire" , "Impulse transmitter - bottle" , "Steel - bottle - neck" , "Sensation transmitter" .)