Old Book found in an outhouse (6)
I believe the answer is:
stable
'an outhouse' is the definition.
(I've seen this before)
'old book found in' is the wordplay.
'old' becomes 'stale' ('stale' can be a synonym of 'old'**).
'book' becomes 'b'.
'found in' indicates putting letters inside.
'stale' enclosing 'b' is 'STABLE'.
(Other definitions for stable that I've seen before include "far from bats?" , "Products all from same place" , "Place of birth" , "providing accommodation for Arabs, perhaps" , "Bleats in a horse-house" .)