Lie in wait possibly? We must be concealed first (7)
I believe the answer is:
initial
'first' is the definition.
(similar in meaning)
'lie in wait possibly? we must be concealed' is the wordplay.
I cannot quite see how this works, but
'in' is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for initial that I've seen before include "Beginning - first letter" , "Primary" , "Name's first letter" , "Start of name" , "Original; beginning" .)