Piggy eats up prickly rodent (9)
I believe the answer is:
porcupine
'prickly rodent' is the definition.
'porcupine' can be an answer for 'rodent' (porcupine is a kind of rodent). I'm not sure about the 'prickly' bit.
'piggy eats up' is the wordplay.
'piggy' becomes 'porcine' (synonyms).
'eats' means one lot of letters goes inside another.
'porcine' placed around 'up' is 'PORCUPINE'.
Can you help me to learn more?
(Other definitions for porcupine that I've seen before include "prickly type" , "Mammal with pointed quills" , "Recoup pin from its bristles" , "Rodent covered in quills" , "Rodent with sharp bristles" .)