A Slav's possibly a humble fellow (6)
I believe the answer is:
vassal
'a humble fellow' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'a slav's possibly' is the wordplay.
'possibly' indicates an anagram.
'a'+'slavs'='aslavs'
'aslavs' is an anagram of 'VASSAL'.
Can you help me to learn more?
(Other definitions for vassal that I've seen before include "Person or nation subject to another" , "Humble servant or subordinate" , "Feudal inferior" , "He owed allegiance and service to a feudal lord" , "Serf, humble servant of old" .)