There is no recognised word in any dictionary, but we could form one by logic. A decahedron is a ten-sided object and decuplicate is a recognised word meaning ten copies. Similarly an icosahedron is a twenty-sided object and so we might say icosuplicate for twenty copies.
quintuplicate sextuplicate septuplicate octuplicate nonuplicate decuplicate
Writing in triplicate.
triplicate
8,000
20% times 100 = 2000% or 20.
quintuplicate sextuplicate septuplicate octuplicate nonuplicate decuplicate
quintuplicate sextuplicate septuplicate octuplicate nonuplicate decuplicate
Triplicate. eg This letter should be done in triplicate.
"triplicate"
triplicate
Writing in triplicate.
You write something out in triplicate.
Writing in triplicate.
triplicate
There is no recognised word for it. Although it would be possible to construct one using Greek (or Latin) prefices, and that would be good for obfuscation or being pretentious, it would not be much use if you wanted to communicate. I would suggest "eighteen-fold".
The future tense is "will triplicate".
Performing a measurement or an experiment three-times is called a triplicate. Triplicate results make statistical analysis better and prevent the possibility of unusual results due to natural/artificial variation.