Mohamed Al-Hakim, 29, allegedly phoned Alya Al-Safar to tell her she must die because of the ‘shame’ she had brought – leaving her too afraid to leave the house.
He had already branded her family ‘bitches and whores’ because of her decision, the court heard.
Miss Al-Safar, 21, had stopped wearing the hijab a few days before the phone call.
She said that Al-Hakim’s mother, her aunt Mardhiya Al-Musawi, ‘wasn’t happy’ that she had stopped covering her hair – a step she had been considering for more than two years.
She received his call when she was with her parents and two younger brothers at their home in Hammersmith, West London.
Al-Hakim allegedly instructed her to play the conversation over a loudspeaker so that they could all listen at about midnight on June 9.
Miss Al-Safar, who did not have her head covered in court but did swear on the Koran, told the jury that Al-Hakim had said: ‘Listen to me carefully, it has been three days and I did not sleep.
Miss Al-Safar's mother, who gave evidence on her behalf, arrived wearing a hijab
‘I have decided not to go out of the house for two weeks.
‘Listen Alya, I am warning you if by the 19th of June you are not wearing the hijab back, I am warning you I will kill you and harm you. I am giving you ten days. You brought shame to your family, you should not have done that.’
Al-Hakim, who denies one charge of making threats to kill, allegedly said he thought the phone call might be taped but he warned her he was ‘not afraid of anything’.
Miss Al-Safar said: ‘He was calm. I was so scared, I really felt scared because my cousin was threatening me.
‘I didn’t know if he was joking, if he was just mad, or if it was true and he would do it.
‘He started shouting, “Listen to me, you had better do what I said.
‘I have seen you on the Edgware Road [a busy street in central London] and if I see you again I will kill you”.
‘He said something about harming my father as well.
‘I was so scared I didn’t want to leave the house and everyone in my family said, “Don’t go out”.’
iss Al-Safar said: ‘Then he said something like, “You all are bitches and whores”.’
Her mother, Fatima Al-Musawi, told the court that Al-Hakim had said: ‘If Alya doesn’t wear the hijab I will kill her or send someone else to kill her.
‘If I see her in Edgware Road, I will kill her dad with her.’
The 44-year-old, who was wearing a hijab, told the jury at Isleworth Crown Court: ‘I was shocked but I knew that he was very nervous, and didn’t believe he would do it.’
Miss Al-Safar’s brother, Khadir Al-Safar, said of the phone call: ‘He said he was tired, sick and ashamed of what my sister had done … to take off her hijab.’
The 20-year-old added that his immediate family supported his sister’s decision, but extended relatives were ‘really mad’.
When asked how his aunt reacted to the news, Mr Al-Safar said: She was so mad, really mad. There were big arguments between my sister and auntie ... lots of talking and swearing.’
George Papageorgis, prosecuting, said: ‘It appears that this cousin, who is the eldest in the immediate vicinity, took exception and gave her an ultimatum.’
The case continues.