Tabloids primarily publish light material (6)
I believe the answer is:
tissue
'light material' is the definition.
(I've seen this before)
'tabloids primarily publish' is the wordplay.
'primarily' indicates taking the first letters.
'publish' becomes 'issue' (synonyms).
The first letter of 'tabloids' is 't'.
't'+'issue'='TISSUE'
(Other definitions for tissue that I've seen before include "Thin fabric" , "Web; fabric" , "Gauzy fabric" , "Paper hanky" , "Basic structural element of an animal or plant" .)