the word ramadan comes from the noun ramad, which refers to "the heat of the stones arising from the intense heat of the sun." the ninth month was named ramadan because when the arabs changed the names of the months from the ancient language, they named them according to the seasons in which they happen to fall.
this month, which used to be called natiq, fell during the summer, the time of extreme heat. 
the merits of ramadan
the prophet (peace be upon him) was reported to have said that "when ramadan comes, the gates of paradise are opened." 
the month of ramadan is a great opportunity for one to do the deeds that could bring him/her closer to paradise.
fasting in ramadan is also an opportunity to atone for one's sins. abu hurayrah quoted the prophet (peace be upon him) as saying, "who ever fasts during the month of ramadan out of sincere faith and hoping for a reward from allah will have all of his previous sins forgiven." 
fasting also provides protection from evil for those who sincerely fast. allah's messenger (peace be upon him) was reported to have said, "fasting is a shield." 
allah has a special reward which he personally gives one who fasts faithfully. abu hurayrah related that the prophet (peace be upon him) quoted allah as saying, "every act of adam's descendants is for themselves, except fasting. it is meant for me alone, and i alone will give the reward for it." 
perhaps the greatest and most unique merit of ramadan lies in the fact that the quran, which is the last and only unchanged book of divine guidance remaining in the world, was revealed during this month. allah states:
"the month of ramadan is the one in which the quran was sent down as a (pure source of) guidance for mankind. in it are clear teachings showing the right way and the criterion (for judging truth and falsehood)."
[noble quran 2:185]
this act of revelation represents the greatest blessing from almighty allah to mankind, who had become steeped in darkness and ignorance since the time of the prior revelation. without this supreme act of mercy, the weakening glimmer of guidance would have gone out completely and oppression would have reigned in all corners of the globe.
 e.w. lane, lane's lexicon, vol. 1, pp. 1156-7.
 collected by al-bukhari (sahih al-bukhari (arabic-english), vol.3, pp. 64-5, no. 115).
 collected by al-bukhari (sahih al-bukhari (arabic-english), vol.3, pp. 69-70, no. 125)
 collected by muslim (sahih muslim (english trans.), vol.2, p.554, no. 2565)
 collected by muslim (sahih muslim (english trans.), vol.2, p.559, no. 2566