The Origin of naming of the months on the moon calendar
The table below shows the names of months in moon calendar from various versions
The Thamud Calendar
(narrated by Al-Azdi)
The Calendar before Islam
(narrated by Al-Bairuni)
The Calendar before Islam
(narrated by Al-Mas’udi)
The Calendar since Islam
The present naming of the moon calendar – according to the strongest stance – have been established since the fifth century AD. It is said that the first person to establish it was Ka’ab Ibn Murra, the fifth grandfather in ascending order of prophet Muhammad -may peace and blessings of Allah be upon him-.
There were five months which name were taken from the seasonal condition of that month (month of Rabiul Awwal, Rabiul Akhir, Jumadil Awal, Jumadil Akhir, and Ramadan). Rabiul Awal and Akhir were taken from word “rabi”, which means “sprout”, since it’s establishment coincided the spring time. Jumadil Awal and Akhir were taken from word “jamad”, which means “frozen”, because the time of these months name establishment coincided the winter time, where waters froze. While Ramadan was taken from word “ramdha”, which means “very hot”, due to it’s establishment coincided the summer time.
The other seven months were named according to the condition of the society and social cycle at that time. Muharram, from the word, “haram”, which means “holy”, since this month is one of the four holy months. Shafar was taken from the word “shifr”, means “zero” or “void”. It was named so, because in this month many of the houses were empty, being left by it’s dwellers who went to war. Rajab, etymologically means “to glorify”, because the ignorant highly glorified this month, and during this month war was strictly forbidden, thus they dubbed this month by “Rajab Al A’sham” (The silent Rajab).
Sha’ban also was named after that fashion. The word sha’ban was taken from the word “sha’bun”, which means “a group” or “a party”. It was termed Sha’ban since during this month, the ignorants would scattered, forming groups, ready for wars, after they left wars in Rajab. Shawwal was taken from the word “syalat”, which means “to uplift”, because this was the time when the she camel lifted their tails, refused to be married by their males. While Dzulqa’dah was taken from the word “al qa’du”, which means “to sit”. In this month, the ignorants started to stay at their homes and they did not make any war, since this month is the beginning of the three consecutive holy months. While Dzulhijja was taken from the name of their type of worshipping in this month, that is pilgrimage to the house of Allah (Hajj). (http://www.ahlalhdeeth.com/vb/showthread.php?t=27755)