A Sanskrit word for "God" or "deity". Esh (ईश in Devanagari script) is also a Sanskrit word for king, head, leader or Lord.
As Esh's meaning in Sanskrit is king, Head, Leader who worshiped as Eshwar (God).
Probably this belief arises from the fact that many Indian Hindu names that end with "Esh or Ish" actually refer to God.