Daughter leaves serious drinker, a sign of things to come (9)
I believe the answer is:
harbinger
'a sign of things to come' is the definition.
(I've seen this before)
'daughter leaves serious drinker' is the wordplay.
'daughter' becomes 'd'.
'leaves' indicates named letters should be taken away.
'serious' becomes 'hard' ('hard' can be similar in meaning to 'serious').
'drinker' becomes 'binger'.
'hard' with 'd' taken out is 'har'.
'har'+'binger'='HARBINGER'
(Other definitions for harbinger that I've seen before include "Precursor" , "One announcing approach" , "Herald - forerunner" , "Early sign" , "omen" .)