Lament that network brought up party drug (5)
I believe the answer is:
dirge
'lament' is the definition.
(synonyms)
'network brought up party drug' is the wordplay.
'network' becomes 'grid' (grid is a kind of network).
'brought up' shows that the letters should be reversed in order (in a down clue, letters go up).
'party drug' becomes 'e' (E is another name for ecstasy. I am not sure about the 'party' bit.).
'grid' back-to-front is 'dirg'.
'dirg'+'e'='DIRGE'
'that' is the link.
Can you help me to learn more?
(Other definitions for dirge that I've seen before include "Funeral lament" , "Sombre music" , "Mournful music" , "Keen; lament" , "Mournful chant" .)