quantity: [14] 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 [17], 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
