I talked to the greybeards about finding a word of power they direct me to arcwind point or something like that where the 3rd word for drain vitality is well I got the word and killed the dragon but the misc quest is still in my quests menu so I can't ask the greybeards for anymore words of power

I have had this same bug.
To avoid it on my new character I travelled there myself before I did the main quest.
Dont know of any way to fix it, soz.

Hah, the joke is on me.
Arngeir sent me there even though I already have the word.