Had to return for a just a share of the old land (5)
I believe the answer is:
judah
'share of the old land' is the definition.
The definition suggests a singular noun which matches the answer.
'had to return for a just a' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'had' is 'dah' which is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for judah that I've seen before include "A son of Jacob and Leah" , "The most powerful of the twelve tribes of Israel" , "Tribe" , "One of 12 tribes of Israel" , "Jewish tribe,kingdom" .)