Live in apparent concealment! (3)
I believe the answer is:
are
'live' is the definition.
('they live' means 'they are')
'in apparent concealment' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ARE' is hidden in the letters of 'apparent concealment'.
(Other definitions for are that I've seen before include "is for more than one" , "Exist; square measure" , "(They/you/we) exist" , "Is, in the plural" , "Unit of land measure equal to 100 square metres" .)