Labour eagerly reveals number one constituent? (4)
I believe the answer is:
urea
'labour' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for urea that I've seen before include "Waste material" , "Waste product of mammals" , "Human waste product" , "wee substance?" , "organic compound" .)