"If he (Modi) does not understand these words, then I can send him a dictionary," Khurshid said.
"I am not his (Modi) doctor, I didn't physically examine him. I meant that he lacks strength to do what he could have done," he added.
However, refusing to apologise for the choice of his words, Khurshid asked: "What should I say if not impotent? Impotent means he failed to do what he was supposed to do.
"Modi was incompetent to stop the violence. He didn't have the capability to stop what happened," the minister said.
Khurshid's fresh salvo against the BJP prime ministerial candidate at a rally in Farrukhabad came as he raised questions about the Gujarat Chief Minister's handling of the post-Godhra riots in 2002. .
Without taking the name of Modi, Khurshid asked why a man who aspires to be the prime minister of the country could not do anything during the 2002 riots.
"Some people came, attacked and went, and you couldn't protect. Are you not a strong man?," he asked.
"We don't accuse you of killing people... Hamara aarop hai ki tum 'napunsak'(impotent) ho. (Our accusation is that you are impotent). You couldn't stop the killers," he added.