So-called oilman works under one without protection (7)
I believe the answer is:
nominal
'so-called' is the definition.
(I've seen this before)
'oilman works under one without protection' is the wordplay.
'works' indicates anagramming the letters (work can mean to twist or convulse).
'under' is a charade indicator (letters next to each other).
'without protection' indicates the central letters (no outside letters).
The middle letter of 'one' is 'n'.
'oilman' anagrammed gives 'ominal'.
'ominal' after 'n' is 'NOMINAL'.
(Other definitions for nominal that I've seen before include "Inconsiderable" , "Trivial" , "Existing in name only" , "Token - lion man (anag)" , "Ostensible" .)