IHS is a traditional abbreviation of the holy name of our Lord, transliterated from Greek into Latin.
In Greek, “Jesus” is written “Ιησούς”, as you can see on Google Translate here:
translate.google.com/#en/el/Jesus
The first Greek letter is “Iota”, or “I” and “i” in both Latin and English. The second Greek letter is “Eta”, or “H” and “h” in both Latin and English. The third Greek letter is “Sigma”, or “S” and “s” in both Latin and English. This is according to the Greek alphabet table here:
en.wikipedia.org/wiki/Greek_alphabet
“Sigma”, which is pronounced and written as “S” and “s” in both Latin and English, can be written with three symbols in Greek: “Σ”, “σ”, or “ς”.
Therefore, an abbreviation of the holy name of Jesus written in Greek, transliterated into Latin and English, is “IHS”.
New Advent clarifies this as well, where it says:
“From the beginning, however, in Christian inscriptions the nomina sacra, or names of Jesus Christ, were shortened by contraction, thus IC and XC or IHS and XPS for Iesous Christos.”
“IHS was sometimes wrongly understood as ‘Jesus Hominum (or Hierosolymae) Salvator’, i.e. Jesus, the Saviour of men (or of Jerusalem=Hierosolyma).”
newadvent.org/cathen/07649a.htm
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