Being a purely lunar calendar, it is not synchronized with the seasons. With an annual drift of 11 or 12 days, the seasonal relation repeats about every 33 Islamic years.
The Hijri months are named as follows in Arabic:
Muḥarram — المحرّم, "forbidden" — so called because it was unlawful (haram) to fight during this month. Muharram is the second most sacred Muslim month and includes the Day of Ashura.
Ṣafar — صفر, "void" — supposedly named because pagan Arabs looted during this month and left the houses empty.
Rabīʿ I (Rabīʿ al-Awwal) — ربيع الأوّل, "the first Spring".
Rabīʿ II (Rabīʿ ath-Thānī) or (Rabīʿ al-Ākhir) — ربيع الثاني or ربيع الآخر, "the second (or last) Spring".
Jumādā I (Jumādā al-Ūlā) — جمادى الأولى, "the first month of parched land".
Jumādā II (Jumādā ath-Thāniya or Jumādā al-Ākhira) — جمادى الآخرة, جمادى الثانية, "the second (or last) month of parched land".
Rajab — رجب, "respect" or "honor". Rajab is another of the sacred months in which fighting was traditionally forbidden.
Shaʿbān — شعبان, "scattered", marking the time of year when Arab tribes dispersed to find water.
Ramaḍān — رمضان, "scorched". Ramadan is the most venerated month of the Hijri calendar, during which Muslims fast between dawn and sunset.
Shawwāl — شوّال, "raised", as she-camels begin to raise their tails during this time of the year, after giving birth.
Dhū al-Qaʿda — ذو القعدة, "the one of truce". Dhu al-Qa'da was another month during which war was banned.
Dhū al-Ḥijja — ذو الحجّة, "the one of pilgrimage", referring to the annual Muslim pilgrimage to Mecca, the Hajj.