Sun and moon letters

In Arabic and Maltese, the consonants are divided into two groups, called the sun letters or solar letters (Arabic:حروف شمسية‎ ḥurūf shamsīyah) and moon letters or lunar letters (حروف قمرية ḥurūf qamarīyah), based on whether or not they assimilate the letter lām (ﻝ l) of a preceding definite article al- (الـ). These names come from the fact that the word for 'the sun', al-shams, pronounced ash-shams, assimilates the lām, while the word for 'the moon', al-qamar, does not.