Hidden article in building on street (7)
I believe the answer is:
stashed
'hidden' is the definition.
(stashed away)
'article in building on street' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'in' indicates putting letters inside.
'building' becomes 'shed' (shed is a kind of building).
'on' means one lot of letters go next to another.
'street' becomes 'st' (abbreviation).
'shed' after 'st' is 'stshed'.
'a' put inside 'stshed' is 'STASHED'.
(Other definitions for stashed that I've seen before include "'Hoarded, squirrelled away (7)'" , "hidden away" , "Saved up for future use" , "hidden from view" , "Stored away in a safe place" .)