moon letter

noun Arabic Grammar.

any letter, as or mīm, representing a consonant that does not assimilate the l of a prefixed definite article.
Compare sun letter.

Origin of moon letter

translation of Arabic al-ḥuruf al-qamorīyah, so called from the use of al-qamar (the moon) to illustrate nonassimilation of l in al the Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019