Sloth unknown in East, captured by young woman (8)
I believe the answer is:
Here is my best explanation:
'sloth' is the definition.
('laziness' can be a synonym of 'sloth')
'unknown in east captured by young woman' is the subsidiary indication.
'unknown' becomes 'z' (algebra).
'east' becomes 'e' ('E' can be a synonym of 'east').
'captured by' is an insertion indicator.
'young woman' becomes 'lass' (lass is a kind of young woman).
'zine' put within 'lass' is 'laziness'.
(Other definitions for laziness that I've seen before include "Sloth", "Idleness" and "Indolence, sloth".)