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.
millionfold
English
Adjective
(-)
A million times so; as, a millionfold dilution, a millionfold increase.
Adverb
(-)
By a factor of a million.
zillionfold
English
Adverb
(-)
(rare) By a factor of a zillion.