Old American stands in for one in household very well (8)
I believe the answer is:
famously
'very well' is the definition.
(thesaurus)
'old american stands in for one in household' is the wordplay.
I cannot quite see how this works, but
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is present in the answer.
'american' could be 'us' (United States) and 'us' is present in the answer.
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for famously that I've seen is " Well - in a way that's well known".)