Still locked, editor's holding up a French competition anyone can enter (8)
I believe the answer is:
unopened
'competition anyone can enter' is the definition.
I can't tell whether this definition defines the answer.
'still locked editor's holding up a french' is the wordplay.
'still' becomes 'open' (I can't justify this - if you can you should give a lot more credence to this answer).
'locked' is an insertion indicator (I've seen this in other clues).
'editor' becomes 'ed' (abbreviation).
'holding up' means one lot of letters go next to another (in a down clue, some letters go below others).
'a french' becomes 'un' ('a' in French).
'ed' put after 'un' is 'uned'.
'open' inserted into 'uned' is 'UNOPENED'.
Can you help me to learn more?
(Other definitions for unopened that I've seen before include "Still closed" , "Remaining closed" , "barred" , "Having held onto seal" , "Remaining sealed" .)