Lock editor up, fool? (7)
I believe the answer is:
dessert
'fool?' is the definition.
(fool is a type of dessert)
'lock editor up' is the wordplay.
'lock' becomes 'tress' (both can mean a piece of hair).
'editor' becomes 'ed' (abbreviation).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'tress'+'ed'='tressed'
'tressed' in reverse letter order is 'DESSERT'.
(Other definitions for dessert that I've seen before include "Christmas pudding maybe" , "Spotted Dick is one" , "Fruit and nuts, perhaps" , "tart?" , "Sweet, afters" .)