Window on left part of church (7)

I believe the answer is:
chancel
'part of church' is the definition.
(area of a church)
'window on left' is the wordplay.
'window on' becomes 'chance' (I can't explain this - if you can you should give a lot more credence to this answer).
'left' becomes 'l' (common abbreviation).
'chance'+'l'='CHANCEL'
Can you help me to learn more?
(Other definitions for chancel that I've seen before include "Part of church near altar" , "Area around the altar of a church" , "where sanctuary may be found" , "screened-off area" , "choir and clergy's area" .)
