Ambitious individual initially employed in a period of growth (8)
I believe the answer is:
aspiring
'ambitious' is the definition.
(similar in meaning)
'individual initially employed in a period of growth' is the wordplay.
'initially' says to take the initial letters.
'employed in' means one lot of letters goes inside another.
'period of growth' becomes 'spring' (when plants grow).
The first letter of 'individual' is 'i'.
'a'+'spring'='aspring'
'i' going within 'aspring' is 'ASPIRING'.
(Other definitions for aspiring that I've seen before include "Having a strong desire to achieve something" , "Hoping" , "Strongly desiring to achieve" , "Striving" , "Having ambition to achieve greater things" .)