Labor leader (3)
I believe the answer is:
ell
'labor leader' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ell that I've seen before include "Old unit of length" , "Old measurement" , "45 inches (cloth)" , "Measure, approx. fourty-five in." , "Once, forty-five inches" .)