Cheese eaten by habitual drunkard unknown for temperance (8)
I believe the answer is:
Here is my best explanation:
'temperance' is the definition.
(sobriety is a kind of temperance)
'cheese eaten by habitual drunkard unknown' is the subsidiary indication.
'cheese' becomes 'brie' (Brie is an example).
'eaten by' means one lot of letters goes inside another.
'habitual drunkard' becomes 'sot' (I've seen this before).
'unknown' becomes 'y' (algebra).
'brie' inserted inside 'sot' is 'sobriet'.
'for' is the link.
(Other definitions for sobriety that I've seen before include "Restraint", "Temperance", "Calmness -- 8 -- by Tories (anag)", "Refraining from", "Serious and self-controlled state, no booze", "Rational, non-intoxicated condition", "Calmness, dispassion", "Calmness, gravity", "restraint" and "Opposite of drunkenness".)