IPA: /ˈsʌbstəns/
KK: /ˈsʌbstəns/
A type of material or matter that has specific qualities or characteristics.
Water is a substance that is essential for life.
Substance is formed from "sub-" (meaning under) and "stare" (meaning to stand). The word refers to that which stands under or supports something, essentially the essence or material of an object.
Think of something that 'stands under' ('sub-') to support it — that's why substance refers to the essential material or essence of something.