One maybe insecure, get nicely covered up (7)
I believe the answer is:
integer
'one' is the definition.
(I've seen this before)
'insecure get nicely covered up' is the wordplay.
'covered' says the answer is hidden in the clue (the answer is covered up by the clue).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'regetni' is hidden in the letters of 'insecure get nicely'.
'regetni' back-to-front is 'INTEGER'.
'maybe' acts as a link.
(Other definitions for integer that I've seen before include "Say one" , "Result of counting" , "Perhaps 60,000" , "Treeing (anag.)" , "Get Erin (anag)" .)