Obama re-activated housing sector (4)
I believe the answer is:
area
'sector' is the definition.
(I've seen this in another clue)
'obama re-activated housing' is the wordplay.
'housing' says the answer is hidden in the clue (part of the clue houses the answer).
'AREA' is hidden within 'obama re activated'.
(Other definitions for area that I've seen before include "topic" , "Space for a specific purpose, say picnic" , "District; plot" , "Speaking formally to (someone)" , "Length multiplied by breadth" .)