Solitary bit of material on editor's desk (4)
I believe the answer is:
lone
'solitary' is the definition.
(I know that solitary can be written as lone)
'bit of material on editor's desk' is the wordplay.
'bit of' says the answer is hidden in the clue.
'LONE' can be found hidden inside 'material on editors desk'.
(Other definitions for lone that I've seen before include "Solitary, sounds like advance" , "The ... Ranger, fictional masked cowboy" , "Single and isolated" , "Companionless" , "He likes to operate by himself" .)