Curiously subtler and almost petty (9)
I believe the answer is:
subaltern
'petty' is the definition.
('subaltern' can be a synonym of 'petty')
'curiously subtler and almost' is the wordplay.
'curiously' indicates an anagram.
'almost' means to remove the last letter (most of the word but not all of it).
'subtler'+'and'='subtlerand'
'subtlerand' with its last letter removed is 'subtleran'.
'subtleran' with letters rearranged gives 'SUBALTERN'.
(Other definitions for subaltern that I've seen before include "Junior officer" , "Lesser official" , "Army officer below the rank of captain" .)