The assumption is the fuss is over a lost point (8)
I believe the answer is:
adoption
'the assumption' is the definition.
(thesaurus)
'the fuss is over a lost point' is the wordplay.
'the fuss' becomes 'ado' (synonyms).
'is over' means one lot of letters go next to another.
'a lost' indicates anagramming the letters.
'point' anagrammed gives 'ption'.
'ado'+'ption'='ADOPTION'
'is' acts as a link.
(Other definitions for adoption that I've seen before include "Acceptance (of, eg, a report)" , "how to create a family" , "Process of taking on another's child" , "The taking on of someone else's child" , "Taking on another's child as one's own" .)