what is the longest word in the old testament (Hebrew letters)?

Would you count the name of Isaiah's son, Mahershalalhashbaz (Is 8:1)? I have no idea what this looks like in Hebrew letters!

The word I have is a different one... Also, are you sure that it is in Isiah chapter 8? because I looked here http://www.kirjasilta.net/tanakh/Yesh.8.html and I can't find the word your referring to.

I looked again, and this time I did find the same that you mentioned. But it's 10 letters long and divided up into three words. The word I'm referring two is 11 letters long, and it's one word, not three.

ashdarpanim ?

The word is והאחשדרפנים. In English pronounced, veha'achshaderpanim. Translates to mean: "and the satraps." (Satrap:a governor of a province under the ancient Persian monarchy.)