Workers' traditional housing long ago (4)
I believe the answer is:
erst
'long ago' is the definition.
(archaic term for formerly or long ago)
'workers' traditional housing' is the wordplay.
'housing' says the answer is hidden in the clue (part of the clue houses the answer).
'ERST' is hidden in the letters of 'workers traditional'.
(Other definitions for erst that I've seen before include "in the past" , "in former times" , "At first; formerly" , "Rest turned formerly" .)