Imam Ibn Katheer, may Allaah have mercy upon him, reported in his Tafseer from Sheykh ‘Alam Ad-Deen As-Sakhaawi in a part he collected and called it Al-Mash-hoor fi Asmaa' Ash-Shuhoor (i.e. Reasons behind the Names of the Lunar Months):
"As for the month of Al-Muharram, it takes its name because it is sacred. For me, it is called so as a confirmation to its sanctity because Arabs used to change its sanctity i.e. make it sacred in one year and make it non-sacred in another.
As for the month of Safar, it takes its name from sifir, which means to be empty, because the houses of the Arabs used to be empty when they go out for travel and business.
As for the month of Rabee‘ Al-Awwal, it was named so because it usually coincides with the spring time.
And the same thing applies to Rabee‘ Al-Aakhir
As for the month of Jumaadaa Al-Oolaa and Jumaadaa Al-Aakhirah, they took their names from Jumad Al-maa' (i.e. water becomes ice). According to their belief, such months does not circulate. This is really untrue because if such months are based on crescents, thus they have to circulate. They may have firstly called them so because these two months occurred while it was cold. You may say: 'Jumaadaa Al-Oolaa or Jumaadaa Al-Awwal and also Jumaadaa Al-’Aakhir or Jumaadaa Al-Aakhirah.'
As for the month of Rajab, it took its name from Tarjeeb (i.e. sanctify and glorification) and because it is a sacred month.
As for the month of Sha‘baan, it is taken from a word which means to split and divide. It took its name because the Arabs would return to fighting upon its onset and divide themselves.
As for the month of Ramadhaan, it is named after Ramdhaa'; Ramdhaa are stones heated by the sun during summer. He said, those who said that it is one of the Names of Allaah The Almighty is actually mistaken and should be disregarded. I have said, there is a Hadeeth was narrated regarding it but it is weak.
As for the month of Shawwaal, it is derived from the lifting (Ar. shayl) of a camel’s tail to ward off flies (because of the extreme heat).
As for the month of Thul-Qa‘dah, it is named such because it was the first sacred month that prohibited fighting. Thus, people sat (refrained from fighting) during that time.
As for the month of Thul-Hijjah, it is named such because the Hajj coincides with it." End quote.
: Alssunnah Net