In the first instance, niceties usually feel fairly sufficient (4)
I believe the answer is:
Here is my best explanation:
'sufficient' is the definition.
(informal way of saying 'enough')
'in the first instance niceties usually feel fairly' is the wordplay.
'in the first instance' indicates taking the first letters.
The initial letters of 'niceties usually feel fairly' is 'NUFF'.