Virtue-signaller supported by low-down element (7)
I believe the answer is:
halogen
'element' is the definition.
(halogen is a kind of element)
'virtue-signaller supported by low-down' is the wordplay.
'virtue-signaller' becomes 'halo' (worn by saints, angels etc).
'supported by' says to put letters next to each other (in a down clue, some letters hold up others).
'low down' becomes 'gen' (both can mean information).
'halo'+'gen'='HALOGEN'
(Other definitions for halogen that I've seen before include "Eg, fluorine or chlorine" , "iodine, perhaps" , "One of group of five elements (used in this type of lamp)" , "Element such as iodine" , "reactive group member" .)