from The Century Dictionary.
- noun The foundress of a summer colony of Aphididæ which is herself born of a winter egg; any female plant-louse that hatches in the spring from a winter egg. The first spring generation of any species is composed of stem-mothers.
Sorry, no etymologies found.
"stem-cell" seems to me the simplest and most suitable, because all the other cells of the body are derived from it, and because it is, in the strictest sense, the stem-father and stem-mother of all the countless generations of cells of which the multicellular organism is to be composed.