“Day of the Lord” is no good as a synonym for “Sunday”?
How about “the Lord’s day,” then?
No, unless you can show once from scripture that Sunday or the first day of the week is referred to as the "day of the Lord" or "the Lord's day". The only instance in all of history that I can find "the lord's day" referring to Sunday is in paganism referring to the day dedicated to the sun god.
BTW The Greek wording for Revelation 1:10 would be "in, on, or among" the Lord's day. That would be consistent with the rest of scripture when "the day of the Lord" or "the Lord's day" refers to a time period.
>>How about “the Lord’s day,” then?<<
Shoe where it is ever in reference to Sunday or any other specific identifiable day.