In ancient times, and a long time after, lots of words were frequently abbreviated, which was very helpful before the printing press, and everything was written out by hand. It was common, therefore, to abbreviate Jesus by using the first three letters. In Greek, that gives you: IHS. But over time, this became Latinized into IHS. Sometimes you’ll also see Ihs, which is just a further development. You might even see IHC, which reflects the fact that a Greek Sigma (S) was sometimes written like a C.
But why did Jesus have a Greek name if he was Jewish? Another great question! The answer is that in the 300 years before Jesus was born, Greek culture became dominant in a large area stretching from Greece all the way to present-day Afghanistan. This was the empire created by Alexander the Great, who died in 323 BC (i.e., Before Christ!). Although Alexander’s lands were divided among his military commanders, Greek culture and language continued to exert great influence all through the region for a long time.
As a result, the New Testament as we have it was written entirely in Greek, as was some of the Old Testament – most of which was written in Hebrew. Even then, in Jesus’ time, the entire Old Testament had been translated into Greek. Even so, many Jews, very likely including Jesus, his mother, Joseph, and many (if not all) of his apostles, would have spoken Aramaic, which was a language derived from Hebrew, which was no longer widely spoken. This shows just how widespread the Greek language was.
One way we know this is by looking at the names of people in the New Testament. Some names are Greek: Andrew and Phillip, for example; others are very Hebrew: Simon and Jude; and still others are Hebrew names that have been rendered in Greek: James (from Jacob), John (from Yochanan). And this is the case with Jesus: it is a Greek rendering of Joshua or Yeshua.
We speak four languages at every Mass! By the way, while you may think the Mass as we are accustomed to it is all in English, that’s not quite right. A small part of it is Greek: Kyrie Eleison, Christe Eleison; a small part is Hebrew: Amen, Alleluia; and sometimes we use Latin, too: Gloria in excelsis Deo, Sanctus, Sanctus, Sanctus, and Agnus Dei. The earliest Christians likewise would have dealt with Aramaic, Greek and Latin. They might have spoken only one, but they would have encountered some of the others as well.
(This is adapted from a recent article in St. Remy Parish Bulletin.)