Informed Comment

HAWAMIM حو اميم
A title given to the seven chapters of the Qur’an which begin with the letters ح Ha م Mim, namely, XL, Suratu ‘l-Mu’min; XLI, Suratu Fussilat; XLII, Suratu ‘sh-Shura; XLIII, Suratu ‘l-Zukhruf; XLIV, Suratu, Suratu ‘d-Dukhan; XLV, Suratu ‘l-Jasiyah; XLVI, Suratu ‘l-Ahqf.
For an explanation of the letters H M are the commencement of these Surah, see HA MIM.
It is related in the Traditions that a man said to the Prophet, “I am old, and my memory is imperfect, and my tongue is stiff;” and the Prophet replied, “Then repeat three of the Surahs beginning with Ha Mim.” (Mishkat, book viii. ch. i. pt. 3.)

Based on Hughes, Dictionary of Islam