zillionfold

As adverbs the difference between millionfold and zillionfold

is that millionfold is by a factor of a million while zillionfold is by a factor of a zillion.

As an adjective millionfold

is a million times so; as, a millionfold dilution, a millionfold increase.

As adverbs the difference between billionfold and zillionfold

is that billionfold is in a billionfold way; by a billion degrees; on a scale of a billion; as, to multiply something a billionfold, to magnify something a billionfold, something which is a billionfold heavier than something else while zillionfold is by a factor of a zillion.

As an adjective billionfold

is a billion times so.

As a noun zillion

is (slang|hyperbole) an unspecified large number (of).

As an adverb zillionfold is

(rare) by a factor of a zillion.