Praise be to Allah.
The scholars (may Allah have mercy on them) differed as to whether shaving and trimming is the same as plucking which come under the heading of namas (plucking facial hair). Some of the scholars – and they are the majority – are of the view that shaving and trimming are like plucking, so it is not permissible to shave or trim the hair of the eyebrows, just as it is haraam to pluck them.
The second view is that the word namas (plucking facial hair) applies to pulling out the hairs only, so it is permissible to remove eyebrow hair by shaving or trimming it. This is the view of the Hanbalis.
It says in al-Mawsoo‘ah al-Fiqhiyyah (14/82): The fuqaha’ are agreed that pulling out the hairs of the eyebrows comes under the heading of plucking facial hair that is prohibited according to the words of the Prophet (blessings and peace of Allah be upon him): “May Allah curse the women who pluck facial hair and those who have that done.” However, they differed with regard to trimming and shaping. The Maalikis and Shaafa‘is are of the view that trimming comes under the same heading as plucking, whereas the Hanbalis are of the view that it is permissible to trim and shave, and that what is prohibited is plucking only. End quote.
For more information, please see the answer to question no. 22393 .
Excluded from the plucking that is forbidden is removal of excess hair that causes harm to the eye or is beyond the bounds of what is normal, such as if the eyebrows attract stares and cause embarrassment to the woman. In that case, she may remove as much as will make them look like the eyebrows of most people, because removing hair from them in this case is more akin to warding off harm, which is by restoring them to their natural state.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: Thinning the eyebrow hair, if it is done by means of plucking, is haraam and is in fact a major sin, because it comes under the heading of plucking facial hair, regarding which the Messenger of Allah (blessings and peace of Allah be upon him) cursed those who do it.
But if it is done by way of trimming or shaving, this is regarded as makrooh by some of the scholars and disallowed by others, who regarded it is coming under the heading of namas, as they said: Namas does not refer only to plucking hair: rather it is general in meaning and applies to any change to facial hair for which Allah has not given permission.
But what we think is appropriate for a woman – even if we say that it is permissible or disliked (makrooh) to thin the eyebrows by trimming or shaving – is that she should not do that unless the hair of the eyebrows is very thick, in such a way that it comes down over the eyes and affects her vision. In that case, there is nothing wrong with removing that which is causing a problem. End quote from Majmoo‘ Fataawa Ibn ‘Uthaymeen (11/133).
And he (may Allah have mercy on him) also said: With regard to thinning the eyebrows, if they are abnormally thick, then there is nothing wrong with it, but if they are only moderately thick, then it is better to leave them as they are, and there is nothing wrong with using scissors or a razor] and the like that does not pull out the hairs, because pulling out the hairs comes under the heading of namas (plucking). End quote from Fataawa Noor ‘ala ad-Darb.
And Allah knows best.