Precise meaning of "fourfold"

Question

I got into a disagreement with someone about the meaning of the word "fourfold." His contention is that it means up to four times as many whereas my contention is that it means four times as many, no less and no more.

I then provided these references to the definitions:

http://www.merriam-webster.com...

1 : being four times as great or as many 
2 : having four units or members

http://www.oxforddictionaries....

1: Four times as great or as numerous:

To which, he responded that the very first definition, "Being four times as great or as many" means, "Being four times as great or as many as four times."

I'm virtually certain it means, "Being four times as great or being four times as many."

Who's right and how do you explain the grammatical differences of the definition?

Answer 1

Stick by your guns. Merriam-Webster’s “four times as great or as many,” like Oxford’s “four times as great or as numerous,” is designed to cover applications to both count and non-count (or mass) nouns. If you have 30 cartridges and I bring you 90 more, you have fourfold what you had before: four times as many. If you have 2.3 liters of fuel in your tank and I pour in 6.9 more, you have fourfold what you had before: four times as much. Cartridges are discrete units, and I cannot give you 2.315 of them; but the fuel is poured in a continuous stream that can be stopped at any point.

In any case, you could well argue that 3 or 3.9 is simply not “as many as” 4.

Answer 2

You're right, on both the interpretation of the word and the interpretation of the definition. You may go pat yourself on the back now...

However, I would generally avoid using fourfold in any situation where you really want to emphasize numerical precision. Just like double, the fact that you're using a word instead of a number seems to imply approximation.

Answer 3

According to the following source the meaning of fourfold, used as an adverb, can also mean: up to four times. Personally I have never met the term used with that meaning.

adj.

• equal to or having four times as many or as much

• composed of four parts

adv.

• by or up to four times as many or as much

Source:Collins English Dictionary