The technical definition of “modern” refers to an era that started centuries ago.
Most people, though, don’t care about technical definitions. Descriptive language versus prescriptive language and all that.
For most people, modern means “of today.”
There are other words that night suit the usage better, but all of them have flaws: comparing a Stradivarius violin to a “contemporary” one would imply the latter violin is contemporary with the former, not with today. “Recent” or “more recent” might work, but they’re even more vague than “modern.” And my own suggestion, “of today,” might preclude anything not literally made on the same calendar day as the statement.
It’s not the perfect word for the concept of “contemporary to today,” but I don’t see that there’s a better one, and trying to prescribe another word — when the use of “modern” for that definition is generally clear — seems like a task doomed to failure.
