Parent at the start of the sixth century? (3)
I believe the answer is:
dad
'parent' is the definition.
(dad can informally mean father)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for dad that I've seen before include "Mum's mate" , "Pa" , "Papa" , "Popular father - a palindrome" , "Relation" .)