Element in magazine online (4)
I believe the answer is:
neon
'element' is the definition.
(I know that neon is a type of element)
'in magazine online' is the wordplay.
'in' indicates a hidden word.
'NEON' is hidden in the letters of 'magazine online'.
(Other definitions for neon that I've seen before include "Element 10, used in lights" , "Element that gives a red glow in a vacuum tube" , "illuminating agent" , "Sign gas" , "Colourless gas, used in lighting" .)