Drinkers' song from master during boozy birthday (9)
I believe the answer is:
dithyramb
'drinkers' song' is the definition.
(hymn dedicated to Dionysus, Greek god of wine)
'master during boozy birthday' is the wordplay.
'master' becomes 'm'.
'during' means one lot of letters goes inside another.
'boozy' indicates an anagram (letters get drunk).
'birthday' with letters rearranged gives 'dithyrab'.
'm' going within 'dithyrab' is 'DITHYRAMB'.
'from' is the link.
(Other definitions for dithyramb that I've seen before include "Song of Ancient Greek" , "spirited lines" , "passionate hymn" , "Ecstatic choral hymn" , "Bacchanalian song" .)