Building up anxious new actor brooding on luck in casting at first (8)
I believe the answer is:
anabolic
'building up' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I can't see?
'anxious new actor brooding on luck in casting at first' is the wordplay.
'anxious new actor brooding' becomes 'anab' (this might be a standard abbreviation of which I'm unaware).
'at first' indicates taking the first letters.
The first letters of 'on luck in casting' is 'olic'.
'anab'+'olic'='ANABOLIC'
Can you help me to learn more?
(Other definitions for anabolic that I've seen before include "-- Steroid" , "Such steroids enhance sporting performance" , "Encouraging muscle growth" , "Promoting the increase of body tissue, as do some steroids" .)