Course porky nurses finish for luncheon (4)
I believe the answer is:
line
'course' is the definition.
(I know that course can be written as line)
'porky nurses finish for luncheon' is the wordplay.
'porky' becomes 'lie' (I've seen this in other clues).
'nurses' is an insertion indicator (nurse can mean to hold onto or harbour).
'finish for' indicates one should take the final letters (the letter which finishes the word).
The last letter of 'luncheon' is 'n'.
'lie' placed around 'n' is 'LINE'.
(Other definitions for line that I've seen before include "Dress" , "Some poetic feet; boundary, when drawn" , "A length without breadth or thickness" , "Fill" , "dash one end to the other" .)