2、quantity:  Latin quantus meant ‘how much’ (it was a compound adjective formed from quī ‘who’). From it was derived the noun quantitās ‘extent, amount’, which passed into English via Old French quantite. Quantum , a noun use of the neuter form of the Latin adjective, originally denoted simply ‘amount’; its specific application to a ‘minimum amount of matter’ was introduced by Max Planck in 1900, and reinforced by Einstein in 1905.=> quantum
4、early 14c., from Old French quantite, cantite (12c., Modern French quantité) and directly from Latin quantitatem (nominative quantitas)"relative greatness or extent,"coined as a loan-translation of Greek posotes (from posos"how great? how much?") from Latin quantus"of what size? how much? how great? what amount?,"correlative pronominal adjective, related to qui"who"(see who). Latin quantitatem also is the source of Italian quantita, Spanish cantidad, Danish and Swedish kvantitet, German quantitat.