The bar on the left, always (5)
I believe the answer is:
Here is my best explanation:
'the bar' is the definition.
(lever is a kind of bar)
'on the left always' is the subsidiary indication.
'on' says to put letters next to each other.
'the left' becomes 'l' (common abbreviation).
'always' becomes 'ever' ('ever' can be a synonym of 'always').
'l' next to 'ever' is 'lever'.
(Other definitions for lever that I've seen before include "Handle", "Bar for prising something", "Operating bar", "Lifting bar pivoted on a fulcrum", "Purchase from bar", "Prise using bar", "Crowbar", "Bar operating machinery", "Pivoting bar, handle" and "Revel in moving bar".)