A Slav’s possibly a humble fellow (6)
I believe the answer is:
vassal
'a humble fellow' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'a slav's possibly' is the wordplay.
'possibly' is an anagram indicator.
'a'+'slavs'='aslavs'
'aslavs' anagrammed gives '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" .)