To make six exact copies of something.
This word is very rare and technical, and it's usually used in a funny or exaggerated way.
Examples:
She sextuplicated the key to the treasure chest.
The scientist sextuplicated the DNA for the experiment.
He sextuplicated the important papers for everyone.
I sextuplicated my favorite toy so I could have one in every room!
The chef sextuplicated the recipe so everyone could have a copy.
I sextuplicated the cookies so I could eat them all day long.