IHS

First recorded before 900; Old English, from Late Latin, from Greek; partial transliteration of the first three letters of Iēsoûs “Jesus”

IHS (also IHC), a monogram or symbol for the name Jesus, is a contraction of the Greek word for Jesus, which in Greek is spelled IHΣΟΥΣ in uncial (majuscule) letters and Iησους in minuscule letters and is transliterated into the Latin alphabet as Iēsus, Jēsus, or Jesus. By the middle of the third century b.c., the letter sigma, which has one uppercase form, Σ, and two lowercase forms, σ (used anywhere except as a final letter) and ς (used as the final letter), had developed the forms C and c. (In the various Cyrillic alphabets, C has the value of Roman S, as in Russian CΠУTНИК “sputnik”). The S in IHS is a Latinized, enlarged form of ς; IHC uses the “new” letter form. IHS and IHC (and other variants) are contractions of IH(ΣΟΥ)Σ and appear in Latin and Greek manuscripts from as early as the 6th century. In the Latin West, the value of eta, H and h, was forgotten, and IHS and IHC were wrongly expanded to Jhesus. Ihs (spelled Iħs) appears in Old English manuscripts in the 9th century.
Later, popular—or just plain wrong—expansions and translations of Latin IHS, IHC include Iēsus Hominum Salvātor “Jesus Savior of Men”; In Hōc Salūs “In this (cross) is Salvation”, and the famous In Hōc Signō Vincēs “In this sign (the cross) shalt thou conquer.” The Latin Christian writer Lactantius (c. 250-c. 325) and the Greek Christian writer Eusebius of Caesarea (c. 260-c. 340) both tell the same basic story of the dream or vision that the emperor Constantine I (Constantine the Great) had while marching with his army, in which he saw in the heavens a bright cross bearing the Greek inscription en toútōi níka “In this (sign) conquer,” rendered into Latin as In Hōc Signō Vincēs, now reduced to the logo for a brand of cigarettes.
In the Middle Ages, IHS was widely used by the Franciscans, and in the Catholic Reformation (the period of Catholic reform that began in 1543 with the Council of Trent), the Jesuits interpreted IHS as Iēsum Habēmus Socium (“We have Jesus as our Companion”).
Two more popular mistakes about the meaning of IHS occur in Ulysses (1922) in Mr. Bloom’s thoughts while he is at Mass: “I have sinned: or no: I have suffered, it is....,” an error that persisted in parochial schools till well past the middle of the 20th century.