Gold rush's start absorbing fellow enthusiast (7)
I believe the answer is:
amateur
'enthusiast' is the definition.
(I've seen this before)
'gold rush's start absorbing fellow' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'start' says to take the initial letters.
'absorbing' is an insertion indicator.
'fellow' becomes 'mate' (I've seen this before).
The initial letter of 'rushs' is 'r'.
'au'+'r'='aur'
'aur' placed around 'mate' is 'AMATEUR'.
(Other definitions for amateur that I've seen before include "He's not professional" , "Inexpert" , "inept player" , "Inept, non-professional" , "One is not professional" .)