News article: "Man sentenced for murdering his 10th wife". What does this mean?

Headlines are not always monointerpretable. They tend to have several interpretations - which is good, they make you read the article for more.

Actually, there are even more possibilities than the two you mention.

• he may have multiple wives, and he killed the tenth one
• he was married ten times - this one he murdered
• he may be married or not, but he kills married women. This was the tenth victim
• he was married ten times, he killed all of his wives

It can even be a combination. From just the headline, the exact meaning can only be guessed, although we can sometimes discard some of the more outrageous interpretations (sometimes).

So, no, we cannot deduce from just the headline how many people were murdered by this man or how many of his victims he was married to. But that is not a bad thing - a headline is usually followed by an article that (one may hope) will tell us exactly what happened.

It says a man was sentenced for murder. The victim was his 10th wife. The rest we don't know.

By itself I would say it's ambiguous.

It could also mean that he had murdered 10 people who were other people's wives. Of course in reality, it's likely to mean that he has murdered one person - who was his 10th wife!