Concealed, out of sight (6)
I believe the answer is:
hidden
This clue is a double definition.
'concealed' is the first definition.
(I know that concealed can be written as hidden)
'out of sight' is the second definition.
(synonyms)
(Other definitions for hidden that I've seen before include "Unseen" , "Covert, obscured" , "Concealed, recondite" , "behind closed doors" , "Abstruse" .)