English word nano- comes from Ancient Greek νάννος, and later Latin nanus ((by extension) small horse. Dwarf.)

Detailed word origin of nano-

Dictionary entry	Language	Definition
νάννος	Ancient Greek (grc)
nanus	Latin (lat)	(by extension) small horse. Dwarf.
nano-	English (eng)	Derived from the nanotechnology industry. In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by 10−9. Symbol: n. Very small.