Once somebody new pursues terms for North Sea gas worker (3-4)
I believe the answer is:
has-been
'once somebody' is the definition.
The definition suggests a singular noun which matches the answer.
'new pursues terms for north sea gas worker' is the wordplay.
'new' becomes 'n' (abbreviation as in New Testament NT).
'pursues' means one lot of letters go next to another.
'terms for' suggests the final letters (I've seen 'term for' mean this (the letter which terminates the word)).
'worker' becomes 'bee' (a worker bee).
The last letters of 'north sea gas' are 'has'.
'has'+'bee'='hasbee'
'n' put after 'hasbee' is 'HAS-BEEN'.
Can you help me to learn more?
(Other definitions for has-been that I've seen before include "One who's past it" , "One-time leading light who's faded" , "One no longer important" , "Faded star?" , "Person no longer famous or successful" .)