Figure millions comes before hospital department's invention (7)
I believe the answer is:
figment
'invention' is the definition.
(thesaurus)
'figure millions comes before hospital department's' is the wordplay.
'figure' becomes 'fig' ('fig' can be a synonym of 'figure'**).
'millions' becomes 'm' (abbreviation).
'comes before' says to put letters next to each other.
'hospital department' becomes 'ent'.
'fig'+'m'+'ent'='FIGMENT'
(Other definitions for figment that I've seen before include "Contrived idea" , "Fantastic notion" , "Imagined object" , "Fancy, fabrication" , "Something that exists only in the imagination" .)