Dhira means that one who is undisturbed in mind. And our disturbance of the mind is due to our ignorance. Suppose I want to go somewhere. Now I am in the station. Actually, it so happened when I came to New York first from India. I was to be dispatched to Butler by the bus station, but I was a new man. I did not know the rules and regulation. Of course, somebody was guiding me. Still, I was very much in disturbed condition, how to get on the bus, how to get the ticket, how... All these. So disturbance of mind is due to our ignorance. So here, a very nice word is used: dhira. Dhira means undisturbed. Undisturbed. So this we should carefully note, that our mind in the material condition is always disturbed.
Lecture on Bhagavad-gita 2.13, New York, March 11, 1966