Content day is finally empty (7)
I believe the answer is:
'content' is the definition.
(I've seen this before)
'day is finally empty' is the wordplay.
'day' becomes 'sat' (abbreviation for Saturday).
'empty' means to remove the middle letters.
'finally' with its middle taken out is 'fy'.
(Other definitions for satisfy that I've seen before include "Fulfil, gratify" , "Be good enough for" , "Satiate" , "Content" , "pay in full" .)