Having principles here once in Rome (and elsewhere round about) (7)
I believe the answer is:
ethical
'having principles here once in rome' is the definition.
The definition suggests a singular noun but the answer is not.
'and elsewhere round about' is the wordplay.
'and elsewhere' becomes 'et al' (I've seen this in another clue).
'round' is an insertion indicator.
'about' becomes 'hic' (I can't explain this - if you can you should believe this answer much more).
'etal' enclosing 'hic' is 'ETHICAL'.
Can you help me to learn more?
(Other definitions for ethical that I've seen before include "Morally correct, in accordance with professional standards" , "Abiding by moral principles" , "Moral, principled" , "In accordance with approved moral standards" , "Morally correct, in accordance with principles" .)