Weekend day is fairly empty in content (7)
I believe the answer is:
satisfy
'content' is the definition.
(I know that content is a more specific form of satisfy)
'weekend day is fairly empty' is the wordplay.
'weekend day' becomes 'Sat' (abbreviation for Saturday).
'empty' suggests removing the centre.
'fairly' with its centre removed is 'fy'.
'sat'+'is'+'fy'='SATISFY'
'in' is the link.
(Other definitions for satisfy that I've seen before include "Fulfil, gratify" , "Meet expectations" , "Make contented or pleased" , "Make contented, fill need" , "Comply with (condition)" .)