Growth of power in the male (5)
I believe the answer is:
maple
'growth' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'power in the male' is the wordplay.
'power' becomes 'p' (symbol in physics).
'in' means one lot of letters goes inside another.
'p' put inside 'male' is 'MAPLE'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for maple that I've seen before include "Ample sort of tree" , "Hard light-coloured wood used for furniture" , "Cathedral city in Devon" , "Leaves on this" , "Tree with winged fruits" .)