Huh? I did spell it correctly.

dec·i·mate /desəˌmāt/ verb

1. kill, destroy, or remove a large percentage or part of. "the project would decimate the fragile wetland wilderness"

The OP is pedentically referring to the original Roman use of the word, which mean to kill/remove a tenth.

Nobody uses the word in that way anymore, but some people want to show how clever they are, so they bring it up.