Keep quiet about fate and sin (5)
I believe the answer is:
sloth
'sin' is the definition.
(I know that sloth is a type of deadly sin)
'keep quiet about fate' is the wordplay.
'keep quiet' becomes 'sh' (as in shushing someone).
'about' indicates putting letters inside.
'fate' becomes 'lot' (synonyms).
'sh' placed around 'lot' is 'SLOTH'.
'and' is the link.
(Other definitions for sloth that I've seen before include "Sluggish creature" , "Torpor" , "One hangs a lot" , "Arboreal animal" , "Aversion to industry" .)