Just ten in this new form (5)
I believe the answer is:
sixth
'just' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'ten in this new form' is the wordplay.
'ten' becomes 'X' (Roman numeral).
'in' means one lot of letters goes inside another.
'new form' is an anagram indicator (I've seen 'new form of' mean this).
'this' is an anagram of 'sith'.
'x' put within 'sith' is 'SIXTH'.
Can you help me to learn more?
(Other definitions for sixth that I've seen before include "Beaten by five" , "fraction" , "ordinal" , "Musical interval from A to F, say" .)