Just ten in this new form (5)
I believe the answer is:
sixth
'just' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
'ten in this new form' is the wordplay.
'ten' becomes 'X' (Roman numeral).
'in' is an insertion indicator.
'new form' is an anagram indicator (I've seen 'new form of' mean this).
'this' with letters rearranged gives 'sith'.
'x' going inside '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" .)