Praise be to Allaah.

Firstly: 

It is not permissible to remove any hair from the eyebrows, whether it is to make them thinner or to reshape them, or for what is called cleaning, which means removing excess or scattered hairs, because that comes under the heading of plucking which is haraam, and concerning which it is narrated that the one who does it is cursed. 

Al-Bukhaari (4886) and Muslim (2125) narrated that ‘Abd-Allaah ibn Mas’ood (may Allaah be pleased with him) said: May Allaah curse the one who does tattoos and the one who has a tattoo done, the one who plucks eyebrows and the one who has her eyebrows plucked, and those who file teeth for the purpose of beautification, changing the creation of Allaah. News of that reached a woman of Banu Asad who was called Umm Ya’qoob, who used to read the Qur’aan. She came to him and said: What is this that I have heard about you cursing the one who does tattoos and the one who has a tattoo done, the one who has her eyebrows plucked, and those who file teeth for the purpose of beautification, changing the creation of Allaah? ‘Abd-Allaah said: Why should I not curse those whom the Messenger of Allaah (blessings and peace of Allaah be upon him) cursed, when it is in the Book of Allaah? The woman said: I have read the Mus-haf from cover to cover and I did not find it. He said: If you had read it you would have found it. Allaah says: “And whatsoever the Messenger (Muhammad صلى الله عليه وسلم) gives you, take it; and whatsoever he forbids you, abstain (from it)” [al-Hashr 59:7]. The woman said: I think that I would see something of that on your wife now. He said: Go and look. So she entered upon the wife of ‘Abd-Allaah and did not see anything. She came to him and said: I did not see anything. He said: If that were the case, we would not live with her. 

See also question number 22393 

And Allaah knows best.