Drift for one thing covers up (5)
I believe the answer is:
tenor
'drift' is the definition.
(I've seen this in another clue)
'for one thing covers up' is the wordplay.
'covers' says the answer is hidden in the clue (I've seen 'covering' mean this).
'up' is a reversal indicator (in down clue: letters go upwards).
'ronet' can be found hidden inside 'for one thing'.
'ronet' reversed gives 'TENOR'.
(Other definitions for tenor that I've seen before include "Male 17" , "Eg, Placido Domingo" , "exact words" , "High voice - low bell" , "Pavarotti, maybe" .)