Beastly line in parental guidance (3)
I believe the answer is:
pig
'line in parental guidance' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for pig that I've seen before include "Farmyard animal" , "Greedy person (colloq.)" , "Porcine animal" , "Boar or sow" , "& 16 Animal pen" .)