I recently needed a word for “multiply by 13” that was parallel to quadruple for “multiply by 4”, so I made up triskadekaduple by analogy with triskadecaphobia. That got me to wondering how you make words for multiples higher than four.
The best answer is probably “don’t.” Your chances of being understood drop sharply after quadruple. But despite the warning sign saying “hic sunt dracones” we forge ahead.
Double, triple, and quadruple are based on Latin names for numbers, so we should keep using Latin prefixes. Next would be quintuple, but I expect you would likely be understood if you said pentuple based on Greek penta-.
Next would be sextuple, septuple, and octuple. These terms are understandable, particularly in the context of multiple births: sextuplets, septuplets, and octuplets.
But now we hit a brick wall. The Latin prefix for nine is novem-, and it’s unlikely anyone would understand novemple or anything like that. The Greek prefix ennea– is no better. Enneauple? Enneaduple?
(The Latin prefix novem– is recognizable from November, which is the 11th month, so does that mean novem– stands for 11? No, November really is the ninth month, or at least it was when the year started in March.)
The only example I can think of for a word starting with ennea– is the enneagram personality classification system.
The prefixes after novem– are equally obscure. But if we jump to 13, some people will have heard of triskadecaphobia. This comes from tris kai deka (three and ten) from Greek. But I would only use triskadecaduple tongue-in-cheek.