Wee! - rubbish clue (9)
I believe the answer is:
minuscule
'wee rubbish clue' is the definition.
'minuscule' can be an answer for 'wee'. I am not certain of the 'rubbish clue' bit.
'wee rubbish clue' is the wordplay.
'wee' becomes 'minus' (I can't justify this - if you can you should believe this answer much more).
'rubbish' indicates anagramming the letters.
'clue' is an anagram of 'cule'.
'minus'+'cule'='MINUSCULE'
(Other definitions for minuscule that I've seen before include "Extremely small, tiny" , "Not important" , "Fine" , "A lower-case letter" , "not capital" .)