Trade function essentially obsolete (7)
I believe the answer is:
defunct
'obsolete' is the definition.
(I've seen this before)
'trade function essentially' is the wordplay.
'essentially' indicates a hidden word (essence can mean the inside of something).
'DEFUNCT' can be found hidden inside 'trade function'.
(Other definitions for defunct that I've seen before include "dead and gone" , "Dead, no longer existing" , "Out of fashion, dead" , "Obsolete" , "Extinct" .)