The - specifies to start from the end and go backwards and the 3 means the third word, so third word from the end. If you need to know how $gettok works in general, then look at /help $gettok in mIRC.
alias word-test {
var %string = word1 word2 word3 word4 word5 word6 word7
var %3rd-last-word = $gettok(%string,$calc($numtok(%string,32) - 2),32)
echo -a This is the 3rd word from the end: %3rd-last-word
}
Usage: /word-test Probably not the best way to do it, but it does work.
Edit, shaefers option is indeed a lot more efficient.
