Nominally faithful pet (4)
I believe the answer is:
fido
'faithful pet' is the definition.
(I've seen this in another clue)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for fido that I've seen before include "it would disperse fog" , "Dog perhaps" , "Typical dog's name" , "Fog disperser" .)