Aeshma is the Younger Avestan

Avestan language

Avestan is an East Iranian language known only from its use as the language of Zoroastrian scripture, i.e. the Avesta, from which it derives its name...

 name of Zoroastrianism's

Zoroastrianism

Zoroastrianism is a religion and philosophy based on the teachings of prophet Zoroaster and was formerly among the world's largest religions. It was probably founded some time before the 6th century BCE in Greater Iran.In Zoroastrianism, the Creator Ahura Mazda is all good, and no evil...

 demon of "wrath." As a hypostatic entity, Aeshma is variously interpreted as "wrath," "rage," and "fury." His standard epithet is "of the bloody mace."

Tri-syllabic aeshma is already attested in Gathic Avestan as aeshema (aēšəma), though not yet - at that early stage - as an entity. The word has an Indo-Iranian root. In the Zoroastrian texts of the 9th-12th centuries, aeshma appears as Middle Persian

Middle Persian

Middle Persian , indigenously known as "Pârsig" sometimes referred to as Pahlavi or Pehlevi, is the Middle Iranian language/ethnolect of Southwestern Iran that during Sassanid times became a prestige dialect and so came to be spoken in other regions as well. Middle Persian is classified as a...

 eshm or kheshm, continuing in Pazend and New Persian as kashm.