Architect left one instrument (7)
I believe the answer is:
pianola
'instrument' is the definition.
(Pianola is an example)
'architect left one' is the wordplay.
'architect' becomes 'piano' (Italian architect Renzo Piano).
'left' becomes 'l' (common abbreviation).
'one' becomes 'a' (a thing is one thing).
'piano'+'l'+'a'='PIANOLA'
(Other definitions for pianola that I've seen before include "Automatic instrument" , "musical instrument" , "Mechanical keyboard instrument" , "Melody Maker" , "Keyboard without a keyboarder!" .)