Number one did shift after work (6)
I believe the answer is:
opiate
'number one' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'did shift after work' is the wordplay.
'did shift' becomes 'iate' (I can't justify this - if you can you should believe this answer much more).
'after' is a charade indicator (letters next to each other).
'work' becomes 'op' (abbreviation for opus).
'iate' after 'op' is 'OPIATE'.
Can you help me to learn more?
(Other definitions for opiate that I've seen before include "Drug from poppies" , "dope" , "painkiller" , "Drug inducing a false sense of contentment" , "description of religion?" .)