We set out to be nice (5)
I believe the answer is:
sweet
'nice' is the definition.
(thesaurus)
'we set out' is the wordplay.
'out' means one lot of letters goes inside another.
'we' put within 'set' is 'SWEET'.
'to be' is the link.
(Other definitions for sweet that I've seen before include "Amiable" , "Candy item" , "Pud" , "Afters" , "It is agreeable" .)