Pleb familiar with monarch (8)
I believe the answer is:
commoner
'pleb' is the definition.
(thesaurus)
'familiar with monarch' is the wordplay.
I cannot quite understand how this works, but
'familiar' could be 'common' (synonyms) and 'common' is present in the answer.
'monarch' could be 'er' (abbreviation for Elizabeth Regina) and 'er' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for commoner that I've seen before include "Less rare; no aristocrat" , "Someone not aristocratic or royal" , "Person who holds no title" , "Someone not belonging to the nobility" , "not so unusual" .)