Drunkenness in baritone ruined absorbing bit of Iolanthe (11)
I believe the answer is:
inebriation
'drunkenness' is the definition.
('inebriation' can be a synonym of 'drunkenness')
'in baritone ruined absorbing bit of iolanthe' is the wordplay.
'ruined' indicates an anagram.
'absorbing' means one lot of letters goes inside another.
'bit of' says to take the initial letters.
The first letter of 'iolanthe' is 'i'.
'in'+'baritone'='inbaritone'
'inbaritone' is an anagram of 'inebration'.
'inebration' placed around 'i' is 'INEBRIATION'.
(Other definitions for inebriation that I've seen before include "Drunkenness" , "Merry state" , "Getting drunk" , "being trashed" .)