A job that’s certainly nice to settle into (8)
I believe the answer is:
sinecure
'a job' is the definition.
(sinecure is a kind of job)
'certainly nice to settle into' is the wordplay.
'certainly' becomes 'sure' ('sure' can be a synonym of 'certainly'**).
'to settle' indicates an anagram (I've seen 'settled' mean this).
'into' is an insertion indicator.
'nice' is an anagram of 'inec'.
'sure' going around 'inec' is 'SINECURE'.
'that's' is the link.
(Other definitions for sinecure that I've seen before include "Paid job requiring little work" , "Paid job with minimal work - insecure (anag)" , "A job that pays well for little work" , "Insecure in cushy job" , "Insecure in easy job" .)