Half of them set up publicity for alcoholic drink (4)
I believe the answer is:
mead
'alcoholic drink' is the definition.
(I've seen this before)
'half of them set up publicity' is the wordplay.
'half of' indicates taking half.
'set up' shows that the letters should be reversed in order.
'publicity' becomes 'ad' (advert).
'them' with half the letters taken is 'em'.
'em' back-to-front is 'me'.
'me'+'ad'='MEAD'
'for' is the link.
(Other definitions for mead that I've seen before include "Cooked joint" , "Honeyed drink; a lea" , "Honey-based alcoholic drink" , "Alcoholic drink of fermented honey and water of old" , "sweet drink" .)